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Campelo F, Lillo JV, von Blume J. Protein condensates in the the secretory pathway: Unraveling biophysical interactions and function. Biophys J 2024; 123:1531-1541. [PMID: 38698644 PMCID: PMC11214006 DOI: 10.1016/j.bpj.2024.04.031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2024] [Revised: 03/23/2024] [Accepted: 04/30/2024] [Indexed: 05/05/2024] Open
Abstract
The emergence of phase separation phenomena among macromolecules has identified biomolecular condensates as fundamental cellular organizers. These condensates concentrate specific components and accelerate biochemical reactions without relying on membrane boundaries. Although extensive studies have revealed a large variety of nuclear and cytosolic membraneless organelles, we are witnessing a surge in the exploration of protein condensates associated with the membranes of the secretory pathway, such as the endoplasmic reticulum and the Golgi apparatus. This review focuses on protein condensates in the secretory pathway and discusses their impact on the organization and functions of this cellular process. Moreover, we explore the modes of condensate-membrane association and the biophysical and cellular consequences of protein condensate interactions with secretory pathway membranes.
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Affiliation(s)
- Felix Campelo
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Castelldefels, Barcelona, Spain.
| | - Javier Vera Lillo
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Castelldefels, Barcelona, Spain
| | - Julia von Blume
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut.
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2
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Campelo F, Tian M, von Blume J. Rediscovering the intricacies of secretory granule biogenesis. Curr Opin Cell Biol 2023; 85:102231. [PMID: 37657367 DOI: 10.1016/j.ceb.2023.102231] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Revised: 08/01/2023] [Accepted: 08/07/2023] [Indexed: 09/03/2023]
Abstract
Regulated secretion, an essential cellular process, relies on secretory granules (SGs) for the controlled release of a diverse range of cargo molecules, including proteins, peptides, hormones, enzymes, and neurotransmitters. SG biogenesis encompasses cargo selection, sorting, packaging, and trafficking, with the trans-Golgi Network (TGN) playing a central role. Research in the last three decades has revealed significant components required for SG biogenesis; however, no cargo receptor transferring granule cargo from the TGN to immature SGs (ISGs) has yet been identified. Consequently, recent research has devoted significant attention to studying receptor-independent cargo sorting mechanisms, shedding new light on the complexities of regulated secretion. Understanding the underlying molecular and biophysical mechanisms behind cargo sorting into ISGs holds great promise for advancing our knowledge of cellular communication and disease mechanisms.
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Affiliation(s)
- Felix Campelo
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860, Castelldefels, Barcelona, Spain
| | - Meng Tian
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | - Julia von Blume
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA.
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3
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Toledo PL, Gianotti AR, Vazquez DS, Ermácora MR. Protein nanocondensates: the next frontier. Biophys Rev 2023; 15:515-530. [PMID: 37681092 PMCID: PMC10480383 DOI: 10.1007/s12551-023-01105-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2023] [Accepted: 07/21/2023] [Indexed: 09/09/2023] Open
Abstract
Over the past decade, myriads of studies have highlighted the central role of protein condensation in subcellular compartmentalization and spatiotemporal organization of biological processes. Conceptually, protein condensation stands at the highest level in protein structure hierarchy, accounting for the assembly of bodies ranging from thousands to billions of molecules and for densities ranging from dense liquids to solid materials. In size, protein condensates range from nanocondensates of hundreds of nanometers (mesoscopic clusters) to phase-separated micron-sized condensates. In this review, we focus on protein nanocondensation, a process that can occur in subsaturated solutions and can nucleate dense liquid phases, crystals, amorphous aggregates, and fibers. We discuss the nanocondensation of proteins in the light of general physical principles and examine the biophysical properties of several outstanding examples of nanocondensation. We conclude that protein nanocondensation cannot be fully explained by the conceptual framework of micron-scale biomolecular condensation. The evolution of nanocondensates through changes in density and order is currently under intense investigation, and this should lead to the development of a general theoretical framework, capable of encompassing the full range of sizes and densities found in protein condensates.
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Affiliation(s)
- Pamela L. Toledo
- Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Roque Sáenz Peña 352, 1876, Bernal, Buenos Aires, Argentina
- Grupo de Biología Estructural y Biotecnología, IMBICE, CONICET, Universidad Nacional de Quilmes, Bernal, Argentina
| | - Alejo R. Gianotti
- Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Roque Sáenz Peña 352, 1876, Bernal, Buenos Aires, Argentina
- Grupo de Biología Estructural y Biotecnología, IMBICE, CONICET, Universidad Nacional de Quilmes, Bernal, Argentina
| | - Diego S. Vazquez
- Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Roque Sáenz Peña 352, 1876, Bernal, Buenos Aires, Argentina
- Grupo de Biología Estructural y Biotecnología, IMBICE, CONICET, Universidad Nacional de Quilmes, Bernal, Argentina
| | - Mario R. Ermácora
- Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Roque Sáenz Peña 352, 1876, Bernal, Buenos Aires, Argentina
- Grupo de Biología Estructural y Biotecnología, IMBICE, CONICET, Universidad Nacional de Quilmes, Bernal, Argentina
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4
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Boyer CK, Bauchle CJ, Zhang J, Wang Y, Stephens SB. Synchronized proinsulin trafficking reveals delayed Golgi export accompanies β-cell secretory dysfunction in rodent models of hyperglycemia. Sci Rep 2023; 13:5218. [PMID: 36997560 PMCID: PMC10063606 DOI: 10.1038/s41598-023-32322-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2022] [Accepted: 03/25/2023] [Indexed: 04/03/2023] Open
Abstract
The pancreatic islet β-cell's preference for release of newly synthesized insulin requires careful coordination of insulin exocytosis with sufficient insulin granule production to ensure that insulin stores exceed peripheral demands for glucose homeostasis. Thus, the cellular mechanisms regulating insulin granule production are critical to maintaining β-cell function. In this report, we utilized the synchronous protein trafficking system, RUSH, in primary β-cells to evaluate proinsulin transit through the secretory pathway leading to insulin granule formation. We demonstrate that the trafficking, processing, and secretion of the proinsulin RUSH reporter, proCpepRUSH, are consistent with current models of insulin maturation and release. Using both a rodent dietary and genetic model of hyperglycemia and β-cell dysfunction, we show that proinsulin trafficking is impeded at the Golgi and coincides with the decreased appearance of nascent insulin granules at the plasma membrane. Ultrastructural analysis of β-cells from diabetic leptin receptor deficient mice revealed gross morphological changes in Golgi structure, including shortened and swollen cisternae, and partial Golgi vesiculation, which are consistent with defects in secretory protein export. Collectively, this work highlights the utility of the proCpepRUSH reporter in studying proinsulin trafficking dynamics and suggests that altered Golgi export function contributes to β-cell secretory defects in the pathogenesis of Type 2 diabetes.
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Affiliation(s)
- Cierra K Boyer
- Department of Neuroscience and Pharmacology, University of Iowa, Iowa City, IA, USA
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA, 52246, USA
| | - Casey J Bauchle
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA, 52246, USA
- Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Iowa, Iowa City, IA, 52246, USA
| | - Jianchao Zhang
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, USA
| | - Yanzhuang Wang
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, USA
- Department of Neurology, School of Medicine, University of Michigan, Ann Arbor, MI, USA
| | - Samuel B Stephens
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA, 52246, USA.
- Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Iowa, Iowa City, IA, 52246, USA.
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5
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Cook TW, Wilstermann AM, Mitchell JT, Arnold NE, Rajasekaran S, Bupp CP, Prokop JW. Understanding Insulin in the Age of Precision Medicine and Big Data: Under-Explored Nature of Genomics. Biomolecules 2023; 13:257. [PMID: 36830626 PMCID: PMC9953665 DOI: 10.3390/biom13020257] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2022] [Revised: 01/20/2023] [Accepted: 01/26/2023] [Indexed: 01/31/2023] Open
Abstract
Insulin is amongst the human genome's most well-studied genes/proteins due to its connection to metabolic health. Within this article, we review literature and data to build a knowledge base of Insulin (INS) genetics that influence transcription, transcript processing, translation, hormone maturation, secretion, receptor binding, and metabolism while highlighting the future needs of insulin research. The INS gene region has 2076 unique variants from population genetics. Several variants are found near the transcriptional start site, enhancers, and following the INS transcripts that might influence the readthrough fusion transcript INS-IGF2. This INS-IGF2 transcript splice site was confirmed within hundreds of pancreatic RNAseq samples, lacks drift based on human genome sequencing, and has possible elevated expression due to viral regulation within the liver. Moreover, a rare, poorly characterized African population-enriched variant of INS-IGF2 results in a loss of the stop codon. INS transcript UTR variants rs689 and rs3842753, associated with type 1 diabetes, are found in many pancreatic RNAseq datasets with an elevation of the 3'UTR alternatively spliced INS transcript. Finally, by combining literature, evolutionary profiling, and structural biology, we map rare missense variants that influence preproinsulin translation, proinsulin processing, dimer/hexamer secretory storage, receptor activation, and C-peptide detection for quasi-insulin blood measurements.
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Affiliation(s)
- Taylor W. Cook
- Department of Pediatrics and Human Development, College of Human Medicine, Michigan State University, Grand Rapids, MI 49503, USA
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI 48824, USA
| | | | - Jackson T. Mitchell
- Department of Pediatrics and Human Development, College of Human Medicine, Michigan State University, Grand Rapids, MI 49503, USA
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI 48824, USA
| | - Nicholas E. Arnold
- Department of Pediatrics and Human Development, College of Human Medicine, Michigan State University, Grand Rapids, MI 49503, USA
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI 48824, USA
| | - Surender Rajasekaran
- Department of Pediatrics and Human Development, College of Human Medicine, Michigan State University, Grand Rapids, MI 49503, USA
- Office of Research, Corewell Health, Grand Rapids, MI 49503, USA
| | - Caleb P. Bupp
- Department of Pediatrics and Human Development, College of Human Medicine, Michigan State University, Grand Rapids, MI 49503, USA
- Division of Medical Genetics, Corewell Health, Grand Rapids, MI 49503, USA
| | - Jeremy W. Prokop
- Department of Pediatrics and Human Development, College of Human Medicine, Michigan State University, Grand Rapids, MI 49503, USA
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI 48824, USA
- Office of Research, Corewell Health, Grand Rapids, MI 49503, USA
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6
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Asai S, Moravcová J, Žáková L, Selicharová I, Hadravová R, Brzozowski AM, Nováček J, Jiráček J. Characterization of insulin crystalline form in isolated β-cell secretory granules. Open Biol 2022; 12:220322. [PMID: 36541100 PMCID: PMC9768635 DOI: 10.1098/rsob.220322] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Insulin is stored in vivo inside the pancreatic β-cell insulin secretory granules. In vitro studies have led to an assumption that high insulin and Zn2+ concentrations inside the pancreatic β-cell insulin secretory granules should promote insulin crystalline state in the form of Zn2+-stabilized hexamers. Electron microscopic images of thin sections of the pancreatic β-cells often show a dense, regular pattern core, suggesting the presence of insulin crystals. However, the structural features of the storage forms of insulin in native preparations of secretory granules are unknown, because of their small size, fragile character and difficult handling. We isolated and investigated the secretory granules from MIN6 cells under near-native conditions, using cryo-electron microscopic (Cryo-EM) techniques. The analysis of these data from multiple intra-granular crystals revealed two different rhomboidal crystal lattices. The minor lattice has unit cell parameters (a ≃ b ≃ 84.0 Å, c ≃ 35.2 Å), similar to in vitro crystallized human 4Zn2+-insulin hexamer, whereas the largely prevalent unit cell has more than double c-axis (a ≃ b ≃ c ≃ 96.5 Å) that probably corresponds to two or three insulin hexamers in the asymmetric unit. Our experimental data show that insulin can be present in pancreatic MIN6 cell granules in a microcrystalline form, probably consisting of 4Zn2+-hexamers of this hormone.
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Affiliation(s)
- Seiya Asai
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 11610 Prague 6, Czech Republic,Department of Biochemistry, Faculty of Science, Charles University, 12840 Prague 2, Czech Republic
| | - Jana Moravcová
- CEITEC, Cryo-Electron Microscopy and Tomography Core Facility, Masaryk University, Kamenice 5, 62500 Bohunice, Czech Republic
| | - Lenka Žáková
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 11610 Prague 6, Czech Republic
| | - Irena Selicharová
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 11610 Prague 6, Czech Republic
| | - Romana Hadravová
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 11610 Prague 6, Czech Republic
| | - Andrzej Marek Brzozowski
- York Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York YO10 5DD, UK
| | - Jiří Nováček
- CEITEC, Cryo-Electron Microscopy and Tomography Core Facility, Masaryk University, Kamenice 5, 62500 Bohunice, Czech Republic
| | - Jiří Jiráček
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 11610 Prague 6, Czech Republic
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7
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Vazquez DS, Toledo PL, Gianotti AR, Ermácora MR. Protein conformation and biomolecular condensates. Curr Res Struct Biol 2022; 4:285-307. [PMID: 36164646 PMCID: PMC9508354 DOI: 10.1016/j.crstbi.2022.09.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2022] [Revised: 09/08/2022] [Accepted: 09/13/2022] [Indexed: 10/27/2022] Open
Abstract
Protein conformation and cell compartmentalization are fundamental concepts and subjects of vast scientific endeavors. In the last two decades, we have witnessed exciting advances that unveiled the conjunction of these concepts. An avalanche of studies highlighted the central role of biomolecular condensates in membraneless subcellular compartmentalization that permits the spatiotemporal organization and regulation of myriads of simultaneous biochemical reactions and macromolecular interactions. These studies have also shown that biomolecular condensation, driven by multivalent intermolecular interactions, is mediated by order-disorder transitions of protein conformation and by protein domain architecture. Conceptually, protein condensation is a distinct level in protein conformational landscape in which collective folding of large collections of molecules takes place. Biomolecular condensates arise by the physical process of phase separation and comprise a variety of bodies ranging from membraneless organelles to liquid condensates to solid-like conglomerates, spanning lengths from mesoscopic clusters (nanometers) to micrometer-sized objects. In this review, we summarize and discuss recent work on the assembly, composition, conformation, material properties, thermodynamics, regulation, and functions of these bodies. We also review the conceptual framework for future studies on the conformational dynamics of condensed proteins in the regulation of cellular processes.
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Affiliation(s)
- Diego S. Vazquez
- Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes and Grupo de Biología Estructural y Biotecnología, IMBICE, CONICET, Universidad Nacional de Quilmes, Argentina
| | - Pamela L. Toledo
- Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes and Grupo de Biología Estructural y Biotecnología, IMBICE, CONICET, Universidad Nacional de Quilmes, Argentina
| | - Alejo R. Gianotti
- Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes and Grupo de Biología Estructural y Biotecnología, IMBICE, CONICET, Universidad Nacional de Quilmes, Argentina
| | - Mario R. Ermácora
- Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes and Grupo de Biología Estructural y Biotecnología, IMBICE, CONICET, Universidad Nacional de Quilmes, Argentina
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8
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Varney MJ, Steyaert W, Coucke PJ, Delanghe JR, Uehling DE, Joseph B, Marcellus R, Al-Awar R, Benovic JL. G protein-coupled receptor kinase 6 (GRK6) regulates insulin processing and secretion via effects on proinsulin conversion to insulin. J Biol Chem 2022; 298:102421. [PMID: 36030052 PMCID: PMC9526158 DOI: 10.1016/j.jbc.2022.102421] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2022] [Revised: 08/16/2022] [Accepted: 08/18/2022] [Indexed: 11/07/2022] Open
Abstract
Recent studies identified a missense mutation in the gene coding for G protein–coupled receptor kinase 6 (GRK6) that segregates with type 2 diabetes (T2D). To better understand how GRK6 might be involved in T2D, we used pharmacological inhibition and genetic knockdown in the mouse β-cell line, MIN6, to determine whether GRK6 regulates insulin dynamics. We show inhibition of GRK5 and GRK6 increased insulin secretion but reduced insulin processing while GRK6 knockdown revealed these same processing defects with reduced levels of cellular insulin. GRK6 knockdown cells also had attenuated insulin secretion but enhanced proinsulin secretion consistent with decreased processing. In support of these findings, we demonstrate GRK6 rescue experiments in knockdown cells restored insulin secretion after glucose treatment. The altered insulin profile appears to be caused by changes in the proprotein convertases, the enzymes responsible for proinsulin to insulin conversion, as GRK6 knockdown resulted in significantly reduced convertase expression and activity. To identify how the GRK6-P384S mutation found in T2D patients might affect insulin processing, we performed biochemical and cell biological assays to study the properties of the mutant. We found that while GRK6-P384S was more active than WT GRK6, it displayed a cytosolic distribution in cells compared to the normal plasma membrane localization of GRK6. Additionally, GRK6 overexpression in MIN6 cells enhanced proinsulin processing, while GRK6-P384S expression had little effect. Taken together, our data show that GRK6 regulates insulin processing and secretion in a glucose-dependent manner and provide a foundation for understanding the contribution of GRK6 to T2D.
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Affiliation(s)
- Matthew J Varney
- Department of Biochemistry and Molecular Biology, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA
| | - Wouter Steyaert
- Department of Human Genetics, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, the Netherlands; Center for Medical Genetics, Ghent University and Ghent University Hospital, Ghent, Belgium
| | - Paul J Coucke
- Center for Medical Genetics, Ghent University and Ghent University Hospital, Ghent, Belgium
| | - Joris R Delanghe
- Department of Diagnostic Sciences, Ghent University, Ghent, Belgium
| | - David E Uehling
- Drug Discovery Program, Ontario Institute for Cancer Research, Toronto, Ontario M5G 0A3, Canada
| | - Babu Joseph
- Drug Discovery Program, Ontario Institute for Cancer Research, Toronto, Ontario M5G 0A3, Canada
| | - Richard Marcellus
- Drug Discovery Program, Ontario Institute for Cancer Research, Toronto, Ontario M5G 0A3, Canada
| | - Rima Al-Awar
- Drug Discovery Program, Ontario Institute for Cancer Research, Toronto, Ontario M5G 0A3, Canada; Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Jeffrey L Benovic
- Department of Biochemistry and Molecular Biology, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA.
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9
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Pizzo F, Mangione MR, Librizzi F, Manno M, Martorana V, Noto R, Vilasi S. The Possible Role of the Type I Chaperonins in Human Insulin Self-Association. Life (Basel) 2022; 12:life12030448. [PMID: 35330199 PMCID: PMC8949404 DOI: 10.3390/life12030448] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2022] [Revised: 03/11/2022] [Accepted: 03/16/2022] [Indexed: 11/16/2022] Open
Abstract
Insulin is a hormone that attends to energy metabolism by regulating glucose levels in the bloodstream. It is synthesised within pancreas beta-cells where, before being released into the serum, it is stored in granules as hexamers coordinated by Zn2+ and further packaged in microcrystalline structures. The group I chaperonin cpn60, known for its assembly-assisting function, is present, together with its cochaperonin cpn10, at each step of the insulin secretory pathway. However, the exact function of the heat shock protein in insulin biosynthesis and processing is still far from being understood. Here we explore the possibility that the molecular machine cpn60/cpn10 could have a role in insulin hexameric assembly and its further crystallization. Moreover, we also evaluate their potential protective effect in pathological insulin aggregation. The experiments performed with the cpn60 bacterial homologue, GroEL, in complex with its cochaperonin GroES, by using spectroscopic methods, microscopy and hydrodynamic techniques, reveal that the chaperonins in vitro favour insulin hexameric organisation and inhibit its aberrant aggregation. These results provide new details in the field of insulin assembly and its related disorders.
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10
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Rohli KE, Boyer CK, Blom SE, Stephens SB. Nutrient Regulation of Pancreatic Islet β-Cell Secretory Capacity and Insulin Production. Biomolecules 2022; 12:335. [PMID: 35204835 PMCID: PMC8869698 DOI: 10.3390/biom12020335] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 02/16/2022] [Accepted: 02/17/2022] [Indexed: 01/27/2023] Open
Abstract
Pancreatic islet β-cells exhibit tremendous plasticity for secretory adaptations that coordinate insulin production and release with nutritional demands. This essential feature of the β-cell can allow for compensatory changes that increase secretory output to overcome insulin resistance early in Type 2 diabetes (T2D). Nutrient-stimulated increases in proinsulin biosynthesis may initiate this β-cell adaptive compensation; however, the molecular regulators of secretory expansion that accommodate the increased biosynthetic burden of packaging and producing additional insulin granules, such as enhanced ER and Golgi functions, remain poorly defined. As these adaptive mechanisms fail and T2D progresses, the β-cell succumbs to metabolic defects resulting in alterations to glucose metabolism and a decline in nutrient-regulated secretory functions, including impaired proinsulin processing and a deficit in mature insulin-containing secretory granules. In this review, we will discuss how the adaptative plasticity of the pancreatic islet β-cell's secretory program allows insulin production to be carefully matched with nutrient availability and peripheral cues for insulin signaling. Furthermore, we will highlight potential defects in the secretory pathway that limit or delay insulin granule biosynthesis, which may contribute to the decline in β-cell function during the pathogenesis of T2D.
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Affiliation(s)
- Kristen E. Rohli
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA 52242, USA; (K.E.R.); (C.K.B.); (S.E.B.)
- Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Iowa, Iowa City, IA 52242, USA
| | - Cierra K. Boyer
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA 52242, USA; (K.E.R.); (C.K.B.); (S.E.B.)
- Department of Neuroscience and Pharmacology, University of Iowa, Iowa City, IA 52242, USA
| | - Sandra E. Blom
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA 52242, USA; (K.E.R.); (C.K.B.); (S.E.B.)
- Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Iowa, Iowa City, IA 52242, USA
| | - Samuel B. Stephens
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA 52242, USA; (K.E.R.); (C.K.B.); (S.E.B.)
- Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Iowa, Iowa City, IA 52242, USA
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11
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Dhayalan B, Chatterjee D, Chen YS, Weiss MA. Structural Lessons From the Mutant Proinsulin Syndrome. Front Endocrinol (Lausanne) 2021; 12:754693. [PMID: 34659132 PMCID: PMC8514764 DOI: 10.3389/fendo.2021.754693] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/06/2021] [Accepted: 09/13/2021] [Indexed: 12/30/2022] Open
Abstract
Insight into folding mechanisms of proinsulin has been provided by analysis of dominant diabetes-associated mutations in the human insulin gene (INS). Such mutations cause pancreatic β-cell dysfunction due to toxic misfolding of a mutant proinsulin and impairment in trans of wild-type insulin secretion. Anticipated by the "Akita" mouse (a classical model of monogenic diabetes mellitus; DM), this syndrome illustrates the paradigm endoreticulum (ER) stress leading to intracellular proteotoxicity. Diverse clinical mutations directly or indirectly perturb native disulfide pairing leading to protein misfolding and aberrant aggregation. Although most introduce or remove a cysteine (Cys; leading in either case to an unpaired thiol group), non-Cys-related mutations identify key determinants of folding efficiency. Studies of such mutations suggest that the hormone's evolution has been constrained not only by structure-function relationships, but also by the susceptibility of its single-chain precursor to impaired foldability. An intriguing hypothesis posits that INS overexpression in response to peripheral insulin resistance likewise leads to chronic ER stress and β-cell dysfunction in the natural history of non-syndromic Type 2 DM. Cryptic contributions of conserved residues to folding efficiency, as uncovered by rare genetic variants, define molecular links between biophysical principles and the emerging paradigm of Darwinian medicine: Biosynthesis of proinsulin at the edge of non-foldability provides a key determinant of "diabesity" as a pandemic disease of civilization.
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Affiliation(s)
| | | | | | - Michael A. Weiss
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, United States
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12
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Germanos M, Gao A, Taper M, Yau B, Kebede MA. Inside the Insulin Secretory Granule. Metabolites 2021; 11:metabo11080515. [PMID: 34436456 PMCID: PMC8401130 DOI: 10.3390/metabo11080515] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2021] [Revised: 08/03/2021] [Accepted: 08/03/2021] [Indexed: 12/19/2022] Open
Abstract
The pancreatic β-cell is purpose-built for the production and secretion of insulin, the only hormone that can remove glucose from the bloodstream. Insulin is kept inside miniature membrane-bound storage compartments known as secretory granules (SGs), and these specialized organelles can readily fuse with the plasma membrane upon cellular stimulation to release insulin. Insulin is synthesized in the endoplasmic reticulum (ER) as a biologically inactive precursor, proinsulin, along with several other proteins that will also become members of the insulin SG. Their coordinated synthesis enables synchronized transit through the ER and Golgi apparatus for congregation at the trans-Golgi network, the initiating site of SG biogenesis. Here, proinsulin and its constituents enter the SG where conditions are optimized for proinsulin processing into insulin and subsequent insulin storage. A healthy β-cell is continually generating SGs to supply insulin in vast excess to what is secreted. Conversely, in type 2 diabetes (T2D), the inability of failing β-cells to secrete may be due to the limited biosynthesis of new insulin. Factors that drive the formation and maturation of SGs and thus the production of insulin are therefore critical for systemic glucose control. Here, we detail the formative hours of the insulin SG from the luminal perspective. We do this by mapping the journey of individual members of the SG as they contribute to its genesis.
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13
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Dhayalan B, Chatterjee D, Chen YS, Weiss MA. Diabetes mellitus due to toxic misfolding of proinsulin variants. Mol Metab 2021:101229. [PMID: 33823319 DOI: 10.1016/j.molmet.2021.101229] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Revised: 03/10/2021] [Accepted: 03/29/2021] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND Dominant mutations in the human insulin gene (INS) lead to pancreatic β-cell dysfunction and diabetes mellitus (DM) due to toxic misfolding of a mutant proinsulin. Analogous to a classical mouse model of monogenic DM ("Akita"), this syndrome highlights the susceptibility of β-cells to endoreticulum (ER) stress due to protein misfolding and aberrant aggregation. SCOPE OF REVIEW Diverse clinical mutations directly or indirectly perturb native disulfide pairing. Whereas most introduce or remove a cysteine (Cys; leading in either case to an unpaired thiol group), non-Cys-related mutations identify key determinants of folding efficiency. Studies of such mutations suggest that the hormone's evolution has been constrained not only by structure-function relationships but also by the susceptibility of its single-chain precursor to impaired foldability. An intriguing hypothesis posits that INS overexpression in response to peripheral insulin resistance likewise leads to chronic ER stress and β-cell dysfunction in the natural history of nonsyndromic Type 2 DM. MAJOR CONCLUSIONS Cryptic contributions of conserved residues to folding efficiency, as uncovered by rare genetic variants, define molecular links between biophysical principles and the emerging paradigm of Darwinian medicine: Biosynthesis of proinsulin at the edge of nonfoldability provides a key determinant of "diabesity" as a pandemic disease of civilization.
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Affiliation(s)
- Balamurugan Dhayalan
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA
| | - Deepak Chatterjee
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA
| | - Yen-Shan Chen
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA
| | - Michael A Weiss
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
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14
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Ma CIJ, Burgess J, Brill JA. Maturing secretory granules: Where secretory and endocytic pathways converge. Adv Biol Regul 2021; 80:100807. [PMID: 33866198 DOI: 10.1016/j.jbior.2021.100807] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2021] [Revised: 03/10/2021] [Accepted: 03/18/2021] [Indexed: 10/21/2022]
Abstract
Secretory granules (SGs) are specialized organelles responsible for the storage and regulated release of various biologically active molecules from the endocrine and exocrine systems. Thus, proper SG biogenesis is critical to normal animal physiology. Biogenesis of SGs starts at the trans-Golgi network (TGN), where immature SGs (iSGs) bud off and undergo maturation before fusing with the plasma membrane (PM). How iSGs mature is unclear, but emerging studies have suggested an important role for the endocytic pathway. The requirement for endocytic machinery in SG maturation blurs the line between SGs and another class of secretory organelles called lysosome-related organelles (LROs). Therefore, it is important to re-evaluate the differences and similarities between SGs and LROs.
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Affiliation(s)
- Cheng-I Jonathan Ma
- Cell Biology Program, The Hospital for Sick Children, PGCRL Building, Room 15.9716, 686 Bay Street, Toronto, Ontario, M5G 0A4, Canada; Institute of Medical Science, University of Toronto, Medical Sciences Building, Room 2374, 1 King's College Circle, Toronto, Ontario, M5S 1A8, Canada
| | - Jason Burgess
- Cell Biology Program, The Hospital for Sick Children, PGCRL Building, Room 15.9716, 686 Bay Street, Toronto, Ontario, M5G 0A4, Canada; Department of Molecular Genetics, University of Toronto, Medical Sciences Building, Room 4396, 1 King's College Circle, Toronto, Ontario, M5S 1A8, Canada
| | - Julie A Brill
- Cell Biology Program, The Hospital for Sick Children, PGCRL Building, Room 15.9716, 686 Bay Street, Toronto, Ontario, M5G 0A4, Canada; Institute of Medical Science, University of Toronto, Medical Sciences Building, Room 2374, 1 King's College Circle, Toronto, Ontario, M5S 1A8, Canada; Department of Molecular Genetics, University of Toronto, Medical Sciences Building, Room 4396, 1 King's College Circle, Toronto, Ontario, M5S 1A8, Canada.
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15
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Dzianová P, Asai S, Chrudinová M, Kosinová L, Potalitsyn P, Šácha P, Hadravová R, Selicharová I, Kříž J, Turkenburg JP, Brzozowski AM, Jiráček J, Žáková L. The efficiency of insulin production and its content in insulin-expressing model β-cells correlate with their Zn 2+ levels. Open Biol 2020; 10:200137. [PMID: 33081637 PMCID: PMC7653362 DOI: 10.1098/rsob.200137] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2020] [Accepted: 09/24/2020] [Indexed: 12/29/2022] Open
Abstract
Insulin is produced and stored inside the pancreatic β-cell secretory granules, where it is assumed to form Zn2+-stabilized oligomers. However, the actual storage forms of this hormone and the impact of zinc ions on insulin production in vivo are not known. Our initial X-ray fluorescence experiment on granules from native Langerhans islets and insulinoma-derived INS-1E cells revealed a considerable difference in the zinc content. This led our further investigation to evaluate the impact of the intra-granular Zn2+ levels on the production and storage of insulin in different model β-cells. Here, we systematically compared zinc and insulin contents in the permanent INS-1E and BRIN-BD11 β-cells and in the native rat pancreatic islets by flow cytometry, confocal microscopy, immunoblotting, specific messenger RNA (mRNA) and total insulin analysis. These studies revealed an impaired insulin production in the permanent β-cell lines with the diminished intracellular zinc content. The drop in insulin and Zn2+ levels was paralleled by a lower expression of ZnT8 zinc transporter mRNA and hampered proinsulin processing/folding in both permanent cell lines. To summarize, we showed that the disruption of zinc homeostasis in the model β-cells correlated with their impaired insulin and ZnT8 production. This indicates a need for in-depth fundamental research about the role of zinc in insulin production and storage.
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Affiliation(s)
- Petra Dzianová
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 116 10 Prague 6, Czech Republic
| | - Seiya Asai
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 116 10 Prague 6, Czech Republic
- Department of Biochemistry, Faculty of Science, Charles University, 12840 Prague 2, Czech Republic
| | - Martina Chrudinová
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 116 10 Prague 6, Czech Republic
| | - Lucie Kosinová
- Laboratory of Pancreatic Islets, Institute for Clinical and Experimental Medicine, Videnska 1958/9, 140 21 Prague, Czech Republic
| | - Pavlo Potalitsyn
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 116 10 Prague 6, Czech Republic
- Department of Biochemistry, Faculty of Science, Charles University, 12840 Prague 2, Czech Republic
| | - Pavel Šácha
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 116 10 Prague 6, Czech Republic
| | - Romana Hadravová
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 116 10 Prague 6, Czech Republic
| | - Irena Selicharová
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 116 10 Prague 6, Czech Republic
| | - Jan Kříž
- Laboratory of Pancreatic Islets, Institute for Clinical and Experimental Medicine, Videnska 1958/9, 140 21 Prague, Czech Republic
| | - Johan P. Turkenburg
- York Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom
| | - Andrzej Marek Brzozowski
- York Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom
| | - Jiří Jiráček
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 116 10 Prague 6, Czech Republic
| | - Lenka Žáková
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 116 10 Prague 6, Czech Republic
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16
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Simultaneous induction of distinct protein phase separation events in multiple subcellular compartments of a single cell. Exp Cell Res 2019; 379:92-109. [DOI: 10.1016/j.yexcr.2019.03.010] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2019] [Revised: 02/18/2019] [Accepted: 03/05/2019] [Indexed: 01/31/2023]
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17
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Guest PC. Biogenesis of the Insulin Secretory Granule in Health and Disease. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1134:17-32. [PMID: 30919330 DOI: 10.1007/978-3-030-12668-1_2] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The secretory granules of pancreatic beta cells are specialized organelles responsible for the packaging, storage and secretion of the vital hormone insulin. The insulin secretory granules also contain more than 100 other proteins including the proteases involved in proinsulin-to insulin conversion, other precursor proteins, minor co-secreted peptides, membrane proteins involved in cell trafficking and ion translocation proteins essential for regulation of the intragranular environment. The synthesis, transport and packaging of these proteins into nascent granules must be carried out in a co-ordinated manner to ensure correct functioning of the granule. The process is regulated by many circulating nutrients such as glucose and can change under different physiological states. This chapter discusses the various processes involved in insulin granule biogenesis with a focus on the granule composition in health and disease.
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Affiliation(s)
- Paul C Guest
- Department of Biochemistry and Tissue Biology, Institute of Biology, University of Campinas (UNICAMP), Campinas, Brazil.
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18
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Mason TO, Shimanovich U. Fibrous Protein Self-Assembly in Biomimetic Materials. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1706462. [PMID: 29883013 DOI: 10.1002/adma.201706462] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2017] [Revised: 03/28/2018] [Indexed: 05/22/2023]
Abstract
Protein self-assembly processes, by which polypeptides interact and independently form multimeric structures, lead to a wide array of different endpoints. Structures formed range from highly ordered molecular crystals to amorphous aggregates. Order arises in the system from a balance between many low-energy processes occurring due to a set of interactions between residues in a chain, between residues in different chains, and between solute and solvent. In Nature, self-assembling protein systems have evolved over millions of years to organize into supramolecular structures, optimized for specific functions, with this propensity determined by the sequence of their constituent amino acids, of which only 20 are encoded in DNA. The structural materials that arise from biological self-assembly can display remarkable mechanical properties, often as a result of hierarchical structure on the nano- and microscales, and much research has been devoted to mimicking and exploiting these properties for a variety of end uses. This work presents a review of a range of studies in which biological functions are effectively reproduced through the design of self-assembling fibrous protein systems.
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Affiliation(s)
- Thomas O Mason
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, 7610001, Israel
| | - Ulyana Shimanovich
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, 7610001, Israel
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19
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Dolui S, Roy A, Pal U, Saha A, Maiti NC. Structural Insight of Amyloidogenic Intermediates of Human Insulin. ACS OMEGA 2018; 3:2452-2462. [PMID: 30023834 PMCID: PMC6045404 DOI: 10.1021/acsomega.7b01776] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2017] [Accepted: 02/16/2018] [Indexed: 05/27/2023]
Abstract
Engaging Raman spectroscopy as a primary tool, we investigated the early events of insulin fibrilization and determined the structural content present in oligomer and protofibrils that are formed as intermediates in the fibril formation pathway. Insulin oligomer, as obtained upon incubation of zinc-free insulin at 60 °C, was mostly spherical in shape, with a diameter of 3-5 nm. Longer incubation produced "necklace"-like beaded protofibrillar assembly species. These intermediates eventually transformed into 5-8 nm thick fibers with smooth surface texture. A broad amide I band in the Raman spectrum of insulin monomer appeared at 1659 cm-1, with a shoulder band at 1676 cm-1. This signature suggested the presence of major helical and extended secondary structure of the protein backbone. In the oligomeric state, the protein maintained its helical imprint (∼50%) and no substantial increment of the compact cross-β-sheet structure was observed. A nonamide helix signature band at 940 cm-1 was present in the oligomeric state, and it was weakened in the fibrillar structure. The 1-anilino-8-naphthalene-sulfonate binding study strongly suggested that a collapse in the tertiary structure, not the major secondary structural realignment, was the dominant factor in the formation of oligomers. In the fibrillar state, the contents of helical and disordered secondary structures decreased significantly and the β-sheet amount increased to ∼62%. The narrow amide I Raman band at 1674 cm-1 in the fibrillar state connoted the formation of vibrationally restricted highly organized β-sheet structure with quaternary realignment into steric-zipped species.
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Affiliation(s)
- Sandip Dolui
- Structural
Biology and Bioinformatics Division, Indian
Institute of Chemical Biology, Council of Scientific and Industrial
Research, 4, Raja S.C. Mullick Road, Kolkata 700032, India
| | - Anupam Roy
- Structural
Biology and Bioinformatics Division, Indian
Institute of Chemical Biology, Council of Scientific and Industrial
Research, 4, Raja S.C. Mullick Road, Kolkata 700032, India
| | - Uttam Pal
- Chemical
Sciences Division, Saha Institute of Nuclear
Physics, 1/AF Bidhannagar, Kolkata 700064, India
| | - Achintya Saha
- Department
of Chemical Technology, University of Calcutta, 92 Acharya Prafulla Chandra Road, Calcutta 700009, India
| | - Nakul C. Maiti
- Structural
Biology and Bioinformatics Division, Indian
Institute of Chemical Biology, Council of Scientific and Industrial
Research, 4, Raja S.C. Mullick Road, Kolkata 700032, India
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20
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Selivanova OM, Grishin SY, Glyakina AV, Sadgyan AS, Ushakova NI, Galzitskaya OV. Analysis of Insulin Analogs and the Strategy of Their Further Development. BIOCHEMISTRY (MOSCOW) 2018; 83:S146-S162. [DOI: 10.1134/s0006297918140122] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Revised: 07/09/2017] [Indexed: 08/30/2023]
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21
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Kowalska M, Rupik W. Ultrastructure of endocrine pancreatic granules during pancreatic differentiation in the grass snake, Natrix natrix L. (Lepidosauria, Serpentes). J Morphol 2017; 279:330-348. [PMID: 29148072 DOI: 10.1002/jmor.20775] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2017] [Revised: 10/30/2017] [Accepted: 11/01/2017] [Indexed: 01/12/2023]
Abstract
We used transmission electron microscopy to study the pancreatic main endocrine cell types in the embryos of the grass snake Natrix natrix L. with focus on the morphology of their secretory granules. The embryonic endocrine part of the pancreas in the grass snake contains four main types of cells (A, B, D, and PP), which is similar to other vertebrates. The B granules contained a moderately electron-dense crystalline-like core that was polygonal in shape and an electron-dense outer zone. The A granules had a spherical electron-dense eccentrically located core and a moderately electron-dense outer zone. The D granules were filled with a moderately electron-dense non-homogeneous content. The PP granules had a spherical electron-dense core with an electron translucent outer zone. Within the main types of granules (A, B, D, PP), different morphological subtypes were recognized that indicated their maturity, which may be related to the different content of these granules during the process of maturation. The sequence of pancreatic endocrine cell differentiation in grass snake embryos differs from that in many vertebrates. In the grass snake embryos, the B and D cells differentiated earlier than A and PP cells. The different sequence of endocrine cell differentiation in snakes and other vertebrates has been related to phylogenetic position and nutrition during early developmental stages.
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Affiliation(s)
- Magdalena Kowalska
- Department of Animal Histology and Embryology, University of Silesia, 9 Bankowa St, Katowice, 40-007, Poland
| | - Weronika Rupik
- Department of Animal Histology and Embryology, University of Silesia, 9 Bankowa St, Katowice, 40-007, Poland
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22
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Du W, Zhou M, Zhao W, Cheng D, Wang L, Lu J, Song E, Feng W, Xue Y, Xu P, Xu T. HID-1 is required for homotypic fusion of immature secretory granules during maturation. eLife 2016; 5. [PMID: 27751232 PMCID: PMC5094852 DOI: 10.7554/elife.18134] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Accepted: 10/17/2016] [Indexed: 02/06/2023] Open
Abstract
Secretory granules, also known as dense core vesicles, are generated at the trans-Golgi network and undergo several maturation steps, including homotypic fusion of immature secretory granules (ISGs) and processing of prehormones to yield active peptides. The molecular mechanisms governing secretory granule maturation are largely unknown. Here, we investigate a highly conserved protein named HID-1 in a mouse model. A conditional knockout of HID-1 in pancreatic β cells leads to glucose intolerance and a remarkable increase in the serum proinsulin/insulin ratio caused by defective proinsulin processing. Large volume three-dimensional electron microscopy and immunofluorescence imaging reveal that ISGs are much more abundant in the absence of HID-1. We further demonstrate that HID-1 deficiency prevented secretory granule maturation by blocking homotypic fusion of immature secretory granules. Our data identify a novel player during the early maturation of immature secretory granules.
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Affiliation(s)
- Wen Du
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Maoge Zhou
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Wei Zhao
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Dongwan Cheng
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Lifen Wang
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Jingze Lu
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Eli Song
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Wei Feng
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Yanhong Xue
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Pingyong Xu
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China.,Key Laboratory of RNA Biology, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Tao Xu
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
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23
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Covaceuszach S, Konarev PV, Cassetta A, Paoletti F, Svergun DI, Lamba D, Cattaneo A. The conundrum of the high-affinity NGF binding site formation unveiled? Biophys J 2015; 108:687-97. [PMID: 25650935 PMCID: PMC4317559 DOI: 10.1016/j.bpj.2014.11.3485] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2014] [Revised: 11/05/2014] [Accepted: 11/07/2014] [Indexed: 11/15/2022] Open
Abstract
The homodimer NGF (nerve growth factor) exerts its neuronal activity upon binding to either or both distinct transmembrane receptors TrkA and p75(NTR). Functionally relevant interactions between NGF and these receptors have been proposed, on the basis of binding and signaling experiments. Namely, a ternary TrkA/NGF/p75(NTR) complex is assumed to be crucial for the formation of the so-called high-affinity NGF binding sites. However, the existence, on the cell surface, of direct extracellular interactions is still a matter of controversy. Here, supported by a small-angle x-ray scattering solution study of human NGF, we propose that it is the oligomerization state of the secreted NGF that may drive the formation of the ternary heterocomplex. Our data demonstrate the occurrence in solution of a concentration-dependent distribution of dimers and dimer of dimers. A head-to-head molecular assembly configuration of the NGF dimer of dimers has been validated. Overall, these findings prompted us to suggest a new, to our knowledge, model for the transient ternary heterocomplex, i.e., a TrkA/NGF/p75(NTR) ligand/receptors molecular assembly with a (2:4:2) stoichiometry. This model would neatly solve the problem posed by the unconventional orientation of p75(NTR) with respect to TrkA, as being found in the crystal structures of the TrkA/NGF and p75(NTR)/NGF complexes.
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Affiliation(s)
- Sonia Covaceuszach
- Istituto di Cristallografia, Consiglio Nazionale delle Ricerche, Trieste, Italy
| | - Petr V Konarev
- European Molecular Biology Laboratory, Hamburg Outstation, Hamburg, Germany; Institute of Crystallography, Russian Academy of Sciences, Moscow, Russia
| | - Alberto Cassetta
- Istituto di Cristallografia, Consiglio Nazionale delle Ricerche, Trieste, Italy
| | | | - Dmitri I Svergun
- European Molecular Biology Laboratory, Hamburg Outstation, Hamburg, Germany
| | - Doriano Lamba
- Istituto di Cristallografia, Consiglio Nazionale delle Ricerche, Trieste, Italy.
| | - Antonino Cattaneo
- European Brain Research Institute, Roma, Italy; Scuola Normale Superiore, Pisa, Italy.
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24
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Pandyarajan V, Smith BJ, Phillips NB, Whittaker L, Cox GP, Wickramasinghe N, Menting JG, Wan ZL, Whittaker J, Ismail-Beigi F, Lawrence MC, Weiss MA. Aromatic anchor at an invariant hormone-receptor interface: function of insulin residue B24 with application to protein design. J Biol Chem 2014; 289:34709-27. [PMID: 25305014 DOI: 10.1074/jbc.m114.608562] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Crystallographic studies of insulin bound to fragments of the insulin receptor have recently defined the topography of the primary hormone-receptor interface. Here, we have investigated the role of Phe(B24), an invariant aromatic anchor at this interface and site of a human mutation causing diabetes mellitus. An extensive set of B24 substitutions has been constructed and tested for effects on receptor binding. Although aromaticity has long been considered a key requirement at this position, Met(B24) was found to confer essentially native affinity and bioactivity. Molecular modeling suggests that this linear side chain can serve as an alternative hydrophobic anchor at the hormone-receptor interface. These findings motivated further substitution of Phe(B24) by cyclohexanylalanine (Cha), which contains a nonplanar aliphatic ring. Contrary to expectations, [Cha(B24)]insulin likewise exhibited high activity. Furthermore, its resistance to fibrillation and the rapid rate of hexamer disassembly, properties of potential therapeutic advantage, were enhanced. The crystal structure of the Cha(B24) analog, determined as an R6 zinc-stabilized hexamer at a resolution of 1.5 Å, closely resembles that of wild-type insulin. The nonplanar aliphatic ring exhibits two chair conformations with partial occupancies, each recapitulating the role of Phe(B24) at the dimer interface. Together, these studies have defined structural requirements of an anchor residue within the B24-binding pocket of the insulin receptor; similar molecular principles are likely to pertain to insulin-related growth factors. Our results highlight in particular the utility of nonaromatic side chains as probes of the B24 pocket and suggest that the nonstandard Cha side chain may have therapeutic utility.
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Affiliation(s)
| | - Brian J Smith
- the La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria 3086, Australia
| | | | | | | | | | - John G Menting
- the Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia, and
| | | | | | | | - Michael C Lawrence
- the Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia, and the Department of Medical Biology, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Michael A Weiss
- From the Departments of Biochemistry, Medicine, and Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106,
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25
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Kumar S, Briguglio JS, Turkewitz AP. An aspartyl cathepsin, CTH3, is essential for proprotein processing during secretory granule maturation in Tetrahymena thermophila. Mol Biol Cell 2014; 25:2444-60. [PMID: 24943840 PMCID: PMC4142616 DOI: 10.1091/mbc.e14-03-0833] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
In animal cells, the assembly of dense cores in secretory granules is controlled by proteolytic processing of proproteins. The same phenomenon occurs in the ciliate Tetrahymena thermophila, but the proteases involved appear to be highly unrelated, suggesting that similar regulatory mechanisms have different molecular origins. In Tetrahymena thermophila, peptides secreted via dense-core granules, called mucocysts, are generated by proprotein processing. We used expression profiling to identify candidate processing enzymes, which localized as cyan fluorescent protein fusions to mucocysts. Of note, the aspartyl cathepsin Cth3p plays a key role in mucocyst-based secretion, since knockdown of this gene blocked proteolytic maturation of the entire set of mucocyst proproteins and dramatically reduced mucocyst accumulation. The activity of Cth3p was eliminated by mutation of two predicted active-site mutations, and overexpression of the wild-type gene, but not the catalytic-site mutant, partially rescued a Mendelian mutant defective in mucocyst proprotein processing. Our results provide the first direct evidence for the role of proprotein processing in this system. Of interest, both localization and the CTH3 disruption phenotype suggest that the enzyme provides non–mucocyst-related functions. Phylogenetic analysis of the T. thermophila cathepsins, combined with prior work on the role of sortilin receptors in mucocyst biogenesis, suggests that repurposing of lysosomal enzymes was an important step in the evolution of secretory granules in ciliates.
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Affiliation(s)
- Santosh Kumar
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637
| | - Joseph S Briguglio
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637
| | - Aaron P Turkewitz
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637
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Briguglio JS, Turkewitz AP. Tetrahymena thermophila: a divergent perspective on membrane traffic. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2014; 322:500-16. [PMID: 24634411 DOI: 10.1002/jez.b.22564] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2013] [Revised: 01/13/2014] [Accepted: 01/22/2014] [Indexed: 12/12/2022]
Abstract
Tetrahymena thermophila, a member of the Ciliates, represents a class of organisms distantly related from commonly used model organisms in cell biology, and thus offers an opportunity to explore potentially novel mechanisms and their evolution. Ciliates, like all eukaryotes, possess a complex network of organelles that facilitate both macromolecular uptake and secretion. The underlying endocytic and exocytic pathways are key mediators of a cell's interaction with its environment, and may therefore show niche-specific adaptations. Our laboratory has taken a variety of approaches to identify key molecular determinants for membrane trafficking pathways in Tetrahymena. Studies of Rab GTPases, dynamins, and sortilin-family receptors substantiate the widespread conservation of some features but also uncover surprising roles for lineage-restricted innovation.
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Affiliation(s)
- Joseph S Briguglio
- The Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois
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Diabetes mellitus due to the toxic misfolding of proinsulin variants. FEBS Lett 2013; 587:1942-50. [PMID: 23669362 DOI: 10.1016/j.febslet.2013.04.044] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2013] [Revised: 04/29/2013] [Accepted: 04/30/2013] [Indexed: 02/06/2023]
Abstract
Dominant mutations in the human insulin gene can lead to pancreatic β-cell dysfunction and diabetes mellitus due to toxic folding of a mutant proinsulin. Analogous to a classical mouse model (the Akita mouse), this monogenic syndrome highlights the susceptibility of human β-cells to endoreticular stress due to protein misfolding and aberrant aggregation. The clinical mutations directly or indirectly perturb native disulfide pairing. Whereas the majority of mutations introduce or remove a cysteine (leading in either case to an unpaired residue), non-cysteine-related mutations identify key determinants of folding efficiency. Studies of such mutations suggest that the evolution of insulin has been constrained not only by its structure and function, but also by the susceptibility of its single-chain precursor to impaired foldability.
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Wang CS, Stewart RJ. Multipart Copolyelectrolyte Adhesive of the Sandcastle Worm, Phragmatopoma californica (Fewkes): Catechol Oxidase Catalyzed Curing through Peptidyl-DOPA. Biomacromolecules 2013; 14:1607-17. [DOI: 10.1021/bm400251k] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Ching Shuen Wang
- Department
of Bioeningeering, University of Utah, 20 South 2030 East,
Room 506C, Salt Lake City, Utah 84112, United States
| | - Russell J. Stewart
- Department
of Bioeningeering, University of Utah, 20 South 2030 East,
Room 506C, Salt Lake City, Utah 84112, United States
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Haataja L, Snapp E, Wright J, Liu M, Hardy AB, Wheeler MB, Markwardt ML, Rizzo M, Arvan P. Proinsulin intermolecular interactions during secretory trafficking in pancreatic β cells. J Biol Chem 2012; 288:1896-906. [PMID: 23223446 DOI: 10.1074/jbc.m112.420018] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Classically, exit from the endoplasmic reticulum (ER) is rate-limiting for secretory protein trafficking because protein folding/assembly occurs there. In this study, we have exploited "hPro-CpepSfGFP," a human proinsulin bearing "superfolder" green fluorescent C-peptide expressed in pancreatic β cells where it is processed to human insulin and CpepSfGFP. Remarkably, steady-state accumulation of hPro-CpepSfGFP and endogenous proinsulin is in the Golgi region, as if final stages of protein folding/assembly were occurring there. The Golgi regional distribution of proinsulin is dynamic, influenced by fasting/refeeding, and increased with β cell zinc deficiency. However, coexpression of ER-entrapped mutant proinsulin-C(A7)Y shifts the steady-state distribution of wild-type proinsulin to the ER. Endogenous proinsulin coprecipitates with hPro-CpepSfGFP and even more so with hProC(A7)Y-CpepSfGFP. Using Cerulean and Venus-tagged proinsulins, we find that both WT-WT and WT-mutant proinsulin pairs exhibit FRET. The data demonstrate that wild-type proinsulin dimerizes within the ER but accumulates at a poorly recognized slow step within the Golgi region, reflecting either slow kinetics of proinsulin hexamerization, steps in formation of nascent secretory granules, or other unknown molecular events. However, in the presence of ongoing misfolding of a subpopulation of proinsulin in β cells, the rate-limiting step in transport of the remaining proinsulin shifts to the ER.
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Affiliation(s)
- Leena Haataja
- Division of Metabolism, Endocrinology, and Diabetes, University of Michigan Medical School, Ann Arbor, Michigan 48105, USA
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Landreh M, Alvelius G, Willander H, Stukenborg JB, Söder O, Johansson J, Jörnvall H. Insulin solubility transitions by pH-dependent interactions with proinsulin C-peptide. FEBS J 2012; 279:4589-97. [PMID: 23106816 DOI: 10.1111/febs.12045] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2012] [Revised: 10/22/2012] [Accepted: 10/22/2012] [Indexed: 12/12/2022]
Abstract
UNLABELLED Proinsulin processing into insulin and C-peptide in the secretory granules of the pancreatic β-cells occurs under mildly acidic conditions and at high peptide concentrations (> 10 mm). Mature insulin has reduced solubility and a propensity to adopt an amyloid-like structure, but is physiologically released as a mixture of a zinc-containing core and a zinc-free, C-peptide-rich fluid phase. C-peptide is known to function in the insulin secretion, but its exact mode of interaction is not established. We now demonstrate that C-peptide in sub-stoichiometric amount versus insulin coprecipitates with insulin at the pH found in secretory vesicles. Precipitation is reversible and the precipitate is dissolved by elevation of the pH. This effect was found to be dependent on relatively conserved glutamate residues in the otherwise poorly conserved C-peptide. Together, the data show that C-peptide has the ability to influence insulin solubility. The physiological pH changes between insulin processing and release sites may therefore affect the quaternary structure of insulin, as well as the phase transitions during insulin sorting and secretion. STRUCTURED DIGITAL ABSTRACT Insulin and C-peptide bind by molecular sieving (View Interaction: 1, 2) C-peptide and Insulin bind by dynamic light scattering (View Interaction: 1, 2) C-peptide and Insulin bind by fluorescence technology (View Interaction: 1, 2, 3, 4).
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Affiliation(s)
- Michael Landreh
- Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-171 77 Stockholm, Sweden
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31
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Hardy AB, Wijesekara N, Genkin I, Prentice KJ, Bhattacharjee A, Kong D, Chimienti F, Wheeler MB. Effects of high-fat diet feeding on Znt8-null mice: differences between β-cell and global knockout of Znt8. Am J Physiol Endocrinol Metab 2012; 302:E1084-96. [PMID: 22338079 PMCID: PMC3774340 DOI: 10.1152/ajpendo.00448.2011] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Genomewide association studies have linked a polymorphism in the zinc transporter 8 (Znt8) gene to higher risk of developing type 2 diabetes. Znt8 is highly expressed in pancreatic β-cells where it is involved in the regulation of zinc transport into granules. However, Znt8 is also expressed in other tissues including α-cells, where its function is as yet unknown. Previous work demonstrated that mice lacking Znt8 globally were more susceptible to diet-induced obesity (Lemaire et al., Proc Natl Acad Sci USA 106: 14872-14877, 2009; Nicolson et al., Diabetes 58: 2070-2083, 2009). Therefore, the main goal of this study was to examine the physiological impact of β-cell-specific Znt8 deficiency in mice during high-fat high-calorie (HFHC) diet feeding. For these studies, we used β-cell-specific Znt8 knockout (Ins2Cre:Znt8loxP/loxP) and whole body Znt8 knockout (Cre-:Znt8(-/-)) mice placed on a HFHC diet for 16 wk. Ins2Cre:Znt8loxP/loxP mice on HFHC diet had similar body weights throughout the study but displayed impaired insulin biosynthesis and secretion and were glucose intolerant compared with littermate control Ins2Cre mice. In contrast, Cre-:Znt8(-/-) mice became remarkably obese, hyperglycemic, hyperinsulinemic, insulin resistant, and glucose intolerant compared with littermate control Cre- mice. These data show that β-cell Znt8 alone does not considerably aggravate weight gain and glucose intolerance during metabolic stress imposed by an HFHC diet. However, global loss of Znt8 is involved in exacerbating diet-induced obesity and resulting insulin resistance, and this may be due to the loss of Znt8 activity in a tissue other than the β-cell. Thus, our data suggest that Znt8 contributes to the risk of developing type 2 diabetes through β-cell- and non-β-cell-specific effects.
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Affiliation(s)
| | | | | | | | | | - D. Kong
- 3Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts; and
| | | | - M. B. Wheeler
- 1Department of Physiology and
- 2Department of Medicine, University of Toronto, Toronto, Ontario, Canada;
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Phillips NB, Whittaker J, Ismail-Beigi F, Weiss MA. Insulin fibrillation and protein design: topological resistance of single-chain analogs to thermal degradation with application to a pump reservoir. J Diabetes Sci Technol 2012; 6:277-88. [PMID: 22538136 PMCID: PMC3380768 DOI: 10.1177/193229681200600210] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Insulin is susceptible to thermal fibrillation, a misfolding process that leads to nonnative cross-β assembly analogous to pathological amyloid deposition. Pharmaceutical formulations are ordinarily protected from such degradation by sequestration of the susceptible monomer within native protein assemblies. With respect to the safety and efficacy of insulin pumps, however, this strategy imposes an intrinsic trade-off between pharmacokinetic goals (rapid absorption and clearance) and the requisite physical properties of a formulation (prolonged shelf life and stability within the reservoir). Available rapid-acting formulations are suboptimal in both respects; susceptibility to fibrillation is exacerbated even as absorption is delayed relative to the ideal specifications of a closed-loop system. To circumvent this molecular trade-off, we exploited structural models of insulin fibrils and amyloidogenic intermediates to define an alternative protective mechanism. Single-chain insulin (SCI) analogs were shown to be refractory to thermal fibrillation with maintenance of biological activity for more than 3 months under conditions that promote the rapid fibrillation and inactivation of insulin. The essential idea exploits an intrinsic incompatibility between SCI topology and the geometry of cross-β assembly. A peptide tether was thus interposed between the A- and B-chains whose length was (a) sufficiently long to provide the "play" needed for induced fit of the hormone on receptor binding and yet (b) sufficiently short to impose a topological barrier to fibrillation. Our findings suggest that ultrastable monomeric SCI analogs may be formulated without protective self-assembly and so permit simultaneous optimization of pharmacokinetics and reservoir life.
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Affiliation(s)
- Nelson B. Phillips
- Department of Biochemistry, Case Western Reserve University School of MedicineCleveland, Ohio
| | - Jonathan Whittaker
- Department of Biochemistry, Case Western Reserve University School of MedicineCleveland, Ohio
| | - Faramarz Ismail-Beigi
- Department of Medicine, Case Western Reserve University School of MedicineCleveland, Ohio
| | - Michael A. Weiss
- Department of Biochemistry, Case Western Reserve University School of MedicineCleveland, Ohio
- Department of Medicine, Case Western Reserve University School of MedicineCleveland, Ohio
- Biomedical Engineering, Case Western Reserve University School of MedicineCleveland, Ohio
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Basford CL, Prentice KJ, Hardy AB, Sarangi F, Micallef SJ, Li X, Guo Q, Elefanty AG, Stanley EG, Keller G, Allister EM, Nostro MC, Wheeler MB. The functional and molecular characterisation of human embryonic stem cell-derived insulin-positive cells compared with adult pancreatic beta cells. Diabetologia 2012; 55:358-71. [PMID: 22075915 DOI: 10.1007/s00125-011-2335-x] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/24/2011] [Accepted: 09/05/2011] [Indexed: 12/26/2022]
Abstract
AIMS/HYPOTHESIS Using a novel directed differentiation protocol, we recently generated up to 25% insulin-producing cells from human embryonic stem cells (hESCs) (insulin(+) cells). At this juncture, it was important to functionally and molecularly characterise these hESC-derived insulin(+) cells and identify key differences and similarities between them and primary beta cells. METHODS We used a new reporter hESC line with green fluorescent protein (GFP) cDNA targeted to the INS locus by homologous recombination (INS (GFP/w)) and an untargeted hESC line (HES2). INS (GFP/w) allowed efficient identification and purification of GFP-producing (INS:GFP(+)) cells. Insulin(+) cells were examined for key features of adult beta cells using microarray, quantitative PCR, secretion assays, imaging and electrophysiology. RESULTS Immunofluorescent staining showed complete co-localisation of insulin with GFP; however, cells were often multihormonal, many with granules containing insulin and glucagon. Electrophysiological recordings revealed variable K(ATP) and voltage-gated Ca(2+) channel activity, and reduced glucose-induced cytosolic Ca(2+) uptake. This translated into defective glucose-stimulated insulin secretion but, intriguingly, appropriate glucagon responses. Gene profiling revealed differences in global gene expression between INS:GFP(+) cells and adult human islets; however, INS:GFP(+) cells had remarkably similar expression of endocrine-lineage transcription factors and genes involved in glucose sensing and exocytosis. CONCLUSIONS/INTERPRETATION INS:GFP(+) cells can be purified from differentiated hESCs, providing a superior source of insulin-producing cells. Genomic analyses revealed that INS:GFP(+) cells collectively resemble immature endocrine cells. However, insulin(+) cells were heterogeneous, a fact that translated into important functional differences within this population. The information gained from this study may now be used to generate new iterations of functioning beta cells that can be purified for transplant.
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Affiliation(s)
- C L Basford
- Division of Cellular and Molecular Biology, Toronto General Research Institute, TMDT, Toronto, ON, Canada
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Zeng G, Shou JJ, Li KK, Zhang YH. In-situ confocal Raman observation of structural changes of insulin crystals in sequential dehydration process. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2011; 1814:1631-40. [DOI: 10.1016/j.bbapap.2011.09.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2011] [Revised: 09/01/2011] [Accepted: 09/02/2011] [Indexed: 11/25/2022]
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Bartolomucci A, Possenti R, Mahata SK, Fischer-Colbrie R, Loh YP, Salton SRJ. The extended granin family: structure, function, and biomedical implications. Endocr Rev 2011; 32:755-97. [PMID: 21862681 PMCID: PMC3591675 DOI: 10.1210/er.2010-0027] [Citation(s) in RCA: 228] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The chromogranins (chromogranin A and chromogranin B), secretogranins (secretogranin II and secretogranin III), and additional related proteins (7B2, NESP55, proSAAS, and VGF) that together comprise the granin family subserve essential roles in the regulated secretory pathway that is responsible for controlled delivery of peptides, hormones, neurotransmitters, and growth factors. Here we review the structure and function of granins and granin-derived peptides and expansive new genetic evidence, including recent single-nucleotide polymorphism mapping, genomic sequence comparisons, and analysis of transgenic and knockout mice, which together support an important and evolutionarily conserved role for these proteins in large dense-core vesicle biogenesis and regulated secretion. Recent data further indicate that their processed peptides function prominently in metabolic and glucose homeostasis, emotional behavior, pain pathways, and blood pressure modulation, suggesting future utility of granins and granin-derived peptides as novel disease biomarkers.
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Affiliation(s)
- Alessandro Bartolomucci
- Department of Integrative Biology and Physiology, University of Minnesota, Minneapolis, Minnesota 55455, USA
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36
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Wijesekara N, Dai FF, Hardy AB, Giglou PR, Bhattacharjee A, Koshkin V, Chimienti F, Gaisano HY, Rutter GA, Wheeler MB. Beta cell-specific Znt8 deletion in mice causes marked defects in insulin processing, crystallisation and secretion. Diabetologia 2010; 53:1656-68. [PMID: 20424817 PMCID: PMC6101216 DOI: 10.1007/s00125-010-1733-9] [Citation(s) in RCA: 228] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/18/2009] [Accepted: 02/05/2010] [Indexed: 02/01/2023]
Abstract
AIMS/HYPOTHESIS Zinc is highly concentrated in pancreatic beta cells, is critical for normal insulin storage and may regulate glucagon secretion from alpha cells. Zinc transport family member 8 (ZnT8) is a zinc efflux transporter that is highly abundant in beta cells. Polymorphisms of ZnT8 (also known as SLC30A8) gene in man are associated with increased risk of type 2 diabetes. While global Znt8 knockout (Znt8KO) mice have been characterised, ZnT8 is also present in other islet cell types and extra-pancreatic tissues. Therefore, it is important to find ways of understanding the role of ZnT8 in beta and alpha cells without the difficulties caused by the confounding effects of ZnT8 in these other tissues. METHODS We generated mice with beta cell-specific (Znt8BKO) and alpha cell-specific (Znt8AKO) knockout of Znt8, and performed in vivo and in vitro characterisation of the phenotypes to determine the functional and anatomical impact of ZnT8 in these cells. Thus we assessed zinc accumulation, insulin granule morphology, insulin biosynthesis and secretion, and glucose homeostasis. RESULTS Znt8BKO mice are glucose-intolerant, have reduced beta cell zinc accumulation and atypical insulin granules. They also display reduced first-phase glucose-stimulated insulin secretion, reduced insulin processing enzyme transcripts and increased proinsulin levels. In contrast, Znt8AKO mice show no evident abnormalities in plasma glucagon and glucose homeostasis. CONCLUSIONS/INTERPRETATION This is the first report of specific beta and alpha cell deletion of Znt8. Our data indicate that while, under the conditions studied, ZnT8 is absolutely essential for proper beta cell function, it is largely dispensable for alpha cell function.
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Affiliation(s)
- N Wijesekara
- Department of Physiology, University of Toronto, 1 King's College Circle Room 3352, Toronto, ON, Canada M5S 1A8
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Paul W, Sharma CP. Tricalcium Phosphate Delayed Release Formulation for Oral Delivery of Insulin: A Proof-of-Concept Study. J Pharm Sci 2008; 97:875-82. [PMID: 17497735 DOI: 10.1002/jps.21012] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Several attempts have been made for delivering insulin orally utilizing several polymers with varying degrees of effectiveness. A major obstacle associated with polymeric delivery system for protein or polypeptide drugs is the poor retention of the structure and its biological activity of encapsulated proteins particularly for the unstable insulin. Calcium phosphate ceramic is considered highly compatible to protein or peptide drugs, particularly insulin. Therefore, an attempt has been made to load insulin in tricalcium phosphate (TCP) microspheres and coat with pH sensitive polymer of methacrylate derivative, and to study the stability and conformational variations of loaded insulin, and finally the biological activity of the formulation in diabetic rats. TCP microspheres were prepared by a standard procedure. Human insulin was loaded in to these porous microspheres by diffusion filling and coated with Eudragit S100. This was subjected to in vitro release studies in simulated fluids and the stability and conformational variations of the released insulin were studied using photon correlation spectroscopy and circular dichroism (CD). Biological activity of the formulation was studied on induced diabetic rats. Insulin released in the intestinal fluid (SIF) maintained the native conformation without showing any aggregation. A dose dependent reduction of blood glucose level (BGL) was achieved in streptozotocin induced diabetic Wistar rats, demonstrating its biological activity. It has been established from this preliminary study that insulin loaded in to TCP microspheres is highly compatible with no degradation or loss of biological activity of loaded insulin. The TCP microsphere based delayed release formulation of insulin has effected a decrease in elevated glucose level in induced diabetic rats, establishing its feasibility towards the development of a noninvasive delivery device.
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Affiliation(s)
- Willi Paul
- Division of Biosurface Technology, Biomedical Technology Wing, Sree Chitra Tirunal Institute for Medical Sciences & Technology, Thiruvananthapuram 695 012, India
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Uchizono Y, Alarcón C, Wicksteed BL, Marsh BJ, Rhodes CJ. The balance between proinsulin biosynthesis and insulin secretion: where can imbalance lead? Diabetes Obes Metab 2007; 9 Suppl 2:56-66. [PMID: 17919179 DOI: 10.1111/j.1463-1326.2007.00774.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Insulin is stored in pancreatic beta-cells in beta-granules. Whenever insulin is secreted in response to a nutrient secretagogue, there is a complementary increase in proinsulin biosynthesis to replenish intracellular insulin stores. This specific nutrient regulation of proinsulin biosynthesis is predominately regulated at the translational level. Recently, a highly conserved cis-element in the 5'-untranslated region (UTR) of preproinsulin mRNA, named ppIGE, has been identified that is required for specific translational regulation of proinsulin biosynthesis. This ppIGE is also found in the 5'-UTR of certain other translationally regulated beta-granule protein mRNAs, including the proinsulin processing endopeptidases, PC1/3 and PC2. This provides a mechanism whereby proinsulin processing is adaptable to changes in proinsulin biosynthesis. However, relatively few beta-granules undergo secretion, with most remaining in the storage pool for approximately 5 days. Aged beta-granules are retired by intracellular degradation mechanisms, either via crinophagy and/or autophagy, as another long-term means of maintaining beta-granule stores at optimal levels. When a disconnection between insulin production and secretion arises, as may occur in type 2 diabetes, autophagy further increases to maintain beta-granule numbers. However, if this increased autophagy becomes chronic, autophagia-mediated cell death occurs that could then contribute to beta-cell loss in type 2 diabetes.
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Affiliation(s)
- Y Uchizono
- Comprehensive Diabetes Center, Department of Medicine, Section of Endocrinology, Diabetes and Metabolism, The University of Chicago, Chicago, IL 60637, USA
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Michael DJ, Cai H, Xiong W, Ouyang J, Chow RH. Mechanisms of peptide hormone secretion. Trends Endocrinol Metab 2006; 17:408-15. [PMID: 17084640 DOI: 10.1016/j.tem.2006.10.011] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/07/2006] [Revised: 10/06/2006] [Accepted: 10/24/2006] [Indexed: 11/21/2022]
Abstract
According to the classical view, peptide hormones are stored in large dense-core vesicles that release all of their cargo rapidly and completely when they fuse with and flatten into the plasma membrane. However, recent imaging studies suggest that this view is too simple. Even after vesicles fuse with the plasma membrane, cells might control the rate of dispersal of vesicle cargo - either by modulating the properties of the fusion pore that connects the vesicle lumen to the extracellular solution or by storing cargo in states that disperse slowly in the extracellular space. Understanding these mechanisms is important, owing to the increasing prevalence of diseases, such as type 2 diabetes mellitus, which arise from insufficient secretion of peptide hormones.
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Affiliation(s)
- Darren J Michael
- Department of Physiology and Biophysics, Keck School of Medicine Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, CA 90089, USA
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Sobota JA, Ferraro F, Bäck N, Eipper BA, Mains RE. Not all secretory granules are created equal: Partitioning of soluble content proteins. Mol Biol Cell 2006; 17:5038-52. [PMID: 17005911 PMCID: PMC1761688 DOI: 10.1091/mbc.e06-07-0626] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Secretory granules carrying fluorescent cargo proteins are widely used to study granule biogenesis, maturation, and regulated exocytosis. We fused the soluble secretory protein peptidylglycine alpha-hydroxylating monooxygenase (PHM) to green fluorescent protein (GFP) to study granule formation. When expressed in AtT-20 or GH3 cells, the PHM-GFP fusion protein partitioned from endogenous hormone (adrenocorticotropic hormone, growth hormone) into separate secretory granule pools. Both exogenous and endogenous granule proteins were stored and released in response to secretagogue. Importantly, we found that segregation of content proteins is not an artifact of overexpression nor peculiar to GFP-tagged proteins. Neither luminal acidification nor cholesterol-rich membrane microdomains play essential roles in soluble content protein segregation. Our data suggest that intrinsic biophysical properties of cargo proteins govern their differential sorting, with segregation occurring during the process of granule maturation. Proteins that can self-aggregate are likely to partition into separate granules, which can accommodate only a few thousand copies of any content protein; proteins that lack tertiary structure are more likely to distribute homogeneously into secretory granules. Therefore, a simple "self-aggregation default" theory may explain the little acknowledged, but commonly observed, tendency for both naturally occurring and exogenous content proteins to segregate from each other into distinct secretory granules.
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Affiliation(s)
- Jacqueline A. Sobota
- *Department of Neuroscience, University of Connecticut Health Center, Farmington, CT 06030-3401; and
| | - Francesco Ferraro
- *Department of Neuroscience, University of Connecticut Health Center, Farmington, CT 06030-3401; and
| | - Nils Bäck
- Department of Anatomy, Institute of Biomedicine, University of Helsinki, FIN-00014, Helsinki, Finland
| | - Betty A. Eipper
- *Department of Neuroscience, University of Connecticut Health Center, Farmington, CT 06030-3401; and
| | - Richard E. Mains
- *Department of Neuroscience, University of Connecticut Health Center, Farmington, CT 06030-3401; and
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Nakagawa SH, Hua QX, Hu SQ, Jia W, Wang S, Katsoyannis PG, Weiss MA. Chiral mutagenesis of insulin. Contribution of the B20-B23 beta-turn to activity and stability. J Biol Chem 2006; 281:22386-22396. [PMID: 16751187 DOI: 10.1074/jbc.m603547200] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Insulin contains a beta-turn (residues B20-B23) interposed between two receptor-binding elements, the central alpha-helix of the B chain (B9-B19) and its C-terminal beta-strand (B24-B28). The turn contains conserved glycines at B20 and B23. Although insulin exhibits marked conformational variability among crystal forms, these glycines consistently maintain positive phi dihedral angles within a classic type-I beta-turn. Because the Ramachandran conformations of GlyB20 and GlyB23 are ordinarily forbidden to L-amino acids, turn architecture may contribute to structure or function. Here, we employ "chiral mutagenesis," comparison of corresponding D- and L-Ala substitutions, to investigate this turn. Control substitutions are introduced at GluB21, a neighboring residue exhibiting a conventional (negative) phi angle. The D- and L-Ala substitutions at B23 are associated with a marked stereospecific difference in activity. Whereas the D-AlaB23 analog retains native activity, the L analog exhibits a 20-fold decrease in receptor binding. By contrast, D- and L-AlaB20 analogs each exhibit high activity. Stereospecific differences between the thermodynamic stabilities of the analogs are nonetheless more pronounced at B20 (delta deltaG(u) 2.0 kcal/mole) than at B23 (delta deltaG(u) 0.7 kcal/mole). Control substitutions at B21 are well tolerated without significant stereospecificity. Chiral mutagenesis thus defines the complementary contributions of these conserved glycines to protein stability (GlyB20) or receptor recognition (GlyB23).
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Affiliation(s)
- Satoe H Nakagawa
- Department of Biochemistry & Molecular Biology, University of Chicago, Chicago, Illinois 60637
| | - Qing-Xin Hua
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, 44106
| | - Shi-Quan Hu
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, 44106
| | - Wenhua Jia
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, 44106
| | - Shuhua Wang
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, 44106
| | - Panayotis G Katsoyannis
- Department of Pharmacology & Biological Chemistry, Mt. Sinai School of Medicine, New York, New York 10029
| | - Michael A Weiss
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, 44106.
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Abstract
Insulin vesicles contain a chemically rich mixture of cargo that includes ions, small molecules, and proteins. At present, it is unclear if all components of this cargo escape from the vesicle at the same rate or to the same extent during exocytosis. Here, we demonstrate through real-time imaging that individual rat and human pancreatic beta-cells secrete insulin in heterogeneous forms that disperse either rapidly or slowly. In healthy pancreatic beta-cells maintained in culture, most vesicles discharge insulin in its fast-release form, a form that leaves individual vesicles in a few hundred milliseconds. The fast-release form of insulin leaves vesicles as rapidly as C-peptide leaves vesicles. Healthy beta-cells also secrete a slow-release form of insulin that leaves vesicles more slowly than C-peptide, over times ranging from seconds to minutes. Individual beta-cells make vesicles with both forms of insulin, though not all vesicles contain both forms of insulin. In addition, we confirm that insulin vesicles store their cargo in two functionally distinct compartments: an acidic solution, or halo, and a condensed core. Thus, our results suggest two important features of the condensed core: 1) It exists in different states among the vesicles undergoing exocytosis and 2) its dissolution determines the availability of insulin during exocytosis.
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Affiliation(s)
- Darren J Michael
- University of Southern California, Keck School of Medicine, Department of Physiology and Biophysics, Los Angeles, CA 90089, USA
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43
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Huang K, Dong J, Phillips NB, Carey PR, Weiss MA. Proinsulin Is Refractory to Protein Fibrillation. J Biol Chem 2005; 280:42345-55. [PMID: 16239223 DOI: 10.1074/jbc.m507110200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Insulin is susceptible to fibrillation, a misfolding process leading to well ordered cross-beta assembly. Protection from fibrillation in beta cells is provided by sequestration of the susceptible monomer within zinc hexamers. We demonstrate that proinsulin is refractory to fibrillation under conditions that promote the rapid fibrillation of zinc-free insulin. Proinsulin fibrils, as probed by Raman microscopy, are nonetheless similar in structure to insulin fibrils. The connecting peptide, although not well ordered in native proinsulin, participates in a fibril-specific beta-sheet. Native insulin and proinsulin exhibit similar free energies of unfolding as inferred from guanidine denaturation studies: relative amyloidogenicities are thus not correlated with global stability. Strikingly, the susceptibility of proinsulin to fibrillation is increased by scission of the connecting peptide at single sites. We thus propose that the connecting peptide constrains a large scale conformational change in the misfolded protein. A tethering mechanism is proposed based on a model of an insulin protofilament derived from electron-microscopic image reconstruction. The proposed relationship between cross-beta assembly and protein topology is supported by studies of single-chain analogs (mini-proinsulin and insulin-like growth factor I) in which foreshortened connecting peptides further retard fibrillation. In addition to its classic function to facilitate disulfide pairing, the connecting peptide may protect beta cells from toxic protein misfolding in the endoplasmic reticulum.
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Affiliation(s)
- Kun Huang
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106, USA
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Mans BJ, Neitz AW. Molecular crowding as a mechanism for tick secretory granule biogenesis. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2004; 34:1187-1193. [PMID: 15522614 DOI: 10.1016/j.ibmb.2004.07.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2004] [Accepted: 07/29/2004] [Indexed: 05/24/2023]
Abstract
During feeding ticks secrete bioactive components into the host to counter-act its immune and hemostatic defense systems. These bioactive components are stored in secretory granules that are secreted during feeding in an exocrine stimulus-response type of mechanism. All proteins destined for secretion are packaged into these granules during granule biogenesis. Up to date no mechanism for granule biogenesis has been proposed, except to note that biogenesis occurs under conditions of high protein and calcium concentrations in an acidic environment. Previously, the most abundant proteins (TSGPs) found in the salivary glands of the soft tick, Ornithodoros savignyi, were suggested to play a part in granule biogenesis, based on their high abundance. The TSGPs are part of the lipocalin family, of which numerous members have been identified in ticks. We consider here the high concentrations of the TSGPs in salivary glands and what effect this will have on the crowded environment inside the secretory granules. It is shown that the TSGPs occur at concentrations that will lead to molecular crowding of which one result is the non-specific aggregation of components to reduce crowding effects. Aggregation of proteins as a mechanism of granule biogenesis has been proposed before, but not in terms of molecular crowding. We thus propose molecular crowding as the general mechanism of granule biogenesis, in tick secretory granules, but can also be extended to other forms of secretory granules in general.
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Affiliation(s)
- Ben J Mans
- The Department of Biochemistry, University of Pretoria, Pretoria 0002, South Africa.
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45
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Zhu YL, Abdo A, Gesmonde JF, Zawalich KC, Zawalich W, Dannies PS. Aggregation and lack of secretion of most newly synthesized proinsulin in non-beta-cell lines. Endocrinology 2004; 145:3840-9. [PMID: 15117881 DOI: 10.1210/en.2003-1512] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Myoblasts transfected with HB10D insulin secrete more hormone than those transfected with wild-type insulin, as published previously, indicating that production of wild-type insulin is not efficient in these cells. The ability of non-beta-cells to produce insulin was examined in several cell lines. In clones of neuroendocrine GH(4)C(1) cells stably transfected with proinsulin, two thirds of (35)S-proinsulin was degraded within 3 h of synthesis, whereas (35)S-prolactin was stable. In transiently transfected neuroendocrine AtT20 cells, half of (35)S-proinsulin was degraded within 3 h after synthesis, whereas (35)S-GH was stable. In transiently transfected fibroblast COS cells, (35)S-proinsulin was stable for longer, but less than 10% was secreted 8 h after synthesis. Proinsulin formed a concentrated patch detected by immunofluorescence in transfected cells that did not colocalize with calreticulin or BiP, markers for the endoplasmic reticulum, but did colocalize with membrin, a marker for the cis-medial Golgi complex. Proinsulin formed a Lubrol-insoluble aggregate within 30 min after synthesis in non-beta-cells but not in INS-1E cells, a beta-cell line that normally produces insulin. More than 45% of (35)S-HB10D proinsulin was secreted from COS cells 3 h after synthesis, and this mutant formed less Lubrol-insoluble aggregate in the cells than did wild-type hormone. These results indicate that proinsulin production from these non-beta-cells is not efficient and that proinsulin aggregates in their secretory pathways. Factors in the environment of the secretory pathway of beta-cells may prevent aggregation of proinsulin to allow efficient production.
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Affiliation(s)
- Yong Lian Zhu
- Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520-8066, USA
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Dannies P. Manipulating the reversible aggregation of protein hormones in secretory granules: potential impact on biopharmaceutical development. BioDrugs 2004; 17:315-24. [PMID: 14498762 DOI: 10.2165/00063030-200317050-00002] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Neuroendocrine cells and other secretory cell types are able to store secretory proteins in a concentrated form for extended periods until the release of large quantities of protein is triggered. The proteins are stored in dense core secretory granules. The dense cores of these granules are made up of large, insoluble aggregates that form by self-association. These aggregates solubilise rapidly into monomeric proteins in their native conformations when released from the cells by exocytosis of secretory granules. Formation of aggregates is an early event in secretory granule formation in at least some cell types. The function of secretory granules containing protein aggregates varies, depending upon the contents. This may occur because recognition of an aspect, such as a surface motif, of the aggregate facilitates correct assembly of the membrane proteins necessary for transport and exocytosis of the granules. Understanding the principles necessary for aggregation of protein hormones may help in the formulation of proteins for clinical use. Formation of aggregates of human prolactin has been investigated both in cells and in solution. In cells, the aggregation of human prolactin requires a mildly acidic pH, and is slowed in the presence of a membrane-permeable chelator of zinc. In solution, the aggregation of human prolactin at mildly acidic pH and physiological concentrations of Zn(2+) resembles that which occurs in cells if the reaction is performed with macromolecular crowding, which will mimic the conditions in cells. The factors causing protein aggregation and the extent to which aggregation plays a role in secretory granule formation are likely to vary with the protein and cell type. Further understanding of the principles involved in forming these aggregates that readily disassociate may enhance the ability to formulate protein preparations. Knowledge of the exact residues involved in the protein : protein interfaces in the aggregates of secretory granule proteins may lead to the ability to use small molecules to interfere with self-association and to regulate the storage of secretory granule proteins.
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Affiliation(s)
- Priscilla Dannies
- Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520-8066, USA.
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Hua QX, Weiss MA. Mechanism of insulin fibrillation: the structure of insulin under amyloidogenic conditions resembles a protein-folding intermediate. J Biol Chem 2004; 279:21449-60. [PMID: 14988398 DOI: 10.1074/jbc.m314141200] [Citation(s) in RCA: 186] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Insulin undergoes aggregation-coupled misfolding to form a cross-beta assembly. Such fibrillation has long complicated its manufacture and use in the therapy of diabetes mellitus. Of interest as a model for disease-associated amyloids, insulin fibrillation is proposed to occur via partial unfolding of a monomeric intermediate. Here, we describe the solution structure of human insulin under amyloidogenic conditions (pH 2.4 and 60 degrees C). Use of an enhanced sensitivity cryogenic probe at high magnetic field avoids onset of fibrillation during spectral acquisition. A novel partial fold is observed in which the N-terminal segments of the A- and B-chains detach from the core. Unfolding of the N-terminal alpha-helix of the A-chain exposes a hydrophobic surface formed by native-like packing of the remaining alpha-helices. The C-terminal segment of the B-chain, although not well ordered, remains tethered to this partial helical core. We propose that detachment of N-terminal segments makes possible aberrant protein-protein interactions in an amyloidogenic nucleus. Non-cooperative unfolding of the N-terminal A-chain alpha-helix resembles that observed in models of proinsulin folding intermediates and foreshadows the extensive alpha --> beta transition characteristic of mature fibrils.
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Affiliation(s)
- Qing-xin Hua
- Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio 44016-4935
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Dong J, Wan Z, Popov M, Carey PR, Weiss MA. Insulin assembly damps conformational fluctuations: Raman analysis of amide I linewidths in native states and fibrils. J Mol Biol 2003; 330:431-42. [PMID: 12823980 DOI: 10.1016/s0022-2836(03)00536-9] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The crystal structure of insulin has been investigated in a variety of dimeric and hexameric assemblies. Interest in dynamics has been stimulated by conformational variability among crystal forms and evidence suggesting that the functional monomer undergoes a conformational change on receptor binding. Here, we employ Raman spectroscopy and Raman microscopy to investigate well-defined oligomeric species: monomeric and dimeric analogs in solution, native T(6) and R(6) hexamers in solution and corresponding polycrystalline samples. Remarkably, linewidths of Raman bands associated with the polypeptide backbone (amide I) exhibit progressive narrowing with successive self-assembly. Whereas dimerization damps fluctuations at an intermolecular beta-sheet, deconvolution of the amide I band indicates that formation of hexamers stabilizes both helical and non-helical elements. Although the structure of a monomer in solution resembles a crystallographic protomer, its encagement in a native assembly damps main-chain fluctuations. Further narrowing of a beta-sheet-specific amide I band is observed on reorganization of insulin in a cross-beta fibril. Enhanced flexibility of the native insulin monomer is in accord with molecular dynamics simulations. Such conformational fluctuations may initiate formation of an amyloidogenic nucleus and enable induced fit on receptor binding.
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Affiliation(s)
- Jian Dong
- Department of Biochemistry, Case Western Reserve University School of Medicine, 10900 Euclid Avenue SOM-W427, Cleveland, OH 44106-4935, USA
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Zhu YL, Conway-Campbell B, Waters MJ, Dannies PS. Prolonged retention after aggregation into secretory granules of human R183H-growth hormone (GH), a mutant that causes autosomal dominant GH deficiency type II. Endocrinology 2002; 143:4243-8. [PMID: 12399418 DOI: 10.1210/en.2002-220575] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Human R183H-GH causes autosomal dominant GH deficiency type II. Because we show here that the mutant hormone is fully bioactive, we have sought to locate an impairment in its progress through the secretory pathway as assessed by pulse chase experiments. Newly synthesized wild-type and R183H-GH were stable when expressed transiently in AtT20 cells, and both formed equivalent amounts of Lubrol-insoluble aggregates within 40 min after synthesis. There was no evidence for intermolecular disulfide bond formation in aggregates of wild-type hormone or the R183H mutant. Both wild-type and R183H-GH were packaged into secretory granules, assessed by the ability of 1 mM BaCl2 to stimulate release and by immunocytochemistry. The mutant differed from wild-type hormone in its retention in the cells after packaging into secretory granules; 50% more R183H-GH than wild-type aggregates were retained in AtT20 cells 120 min after synthesis, and stimulated release of R183H-GH or a mixture of R183H-GH and wild-type that had been retained in the cell was reduced. The longer retention of R183H-GH aggregates indicates that a single point mutation in a protein contained in secretory granules affects the rate of secretory granule release.
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Affiliation(s)
- Yong Lian Zhu
- Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520, USA
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50
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Haddad A, Bowman GR, Turkewitz AP. New class of cargo protein in Tetrahymena thermophila dense core secretory granules. EUKARYOTIC CELL 2002; 1:583-93. [PMID: 12456006 PMCID: PMC117993 DOI: 10.1128/ec.1.4.583-593.2002] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Regulated exocytosis of dense core secretory granules releases biologically active proteins in a stimulus-dependent fashion. The packaging of the cargo within newly forming granules involves a transition: soluble polypeptides condense to form water-insoluble aggregates that constitute the granule cores. Following exocytosis, the cores generally disassemble to diffuse in the cell environment. The ciliates Tetrahymena thermophila and Paramecium tetraurelia have been advanced as genetically manipulatable systems for studying exocytosis via dense core granules. However, all of the known granule proteins in these organisms condense to form the architectural units of lattices that are insoluble both before and after exocytosis. Using an approach designed to detect new granule proteins, we have now identified Igr1p (induced during granule regeneration). By structural criteria, it is unrelated to the previously characterized lattice-forming proteins. It is distinct in that it is capable of dissociating from the insoluble lattice following secretion and therefore represents the first diffusible protein identified in ciliate granules.
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Affiliation(s)
- Alex Haddad
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637, USA
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