1
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Little M, Ortlund EA. Structure, function, and lipid sensing activity in the thioesterase superfamily. Biochem Soc Trans 2024; 52:1565-1577. [PMID: 39140379 DOI: 10.1042/bst20230313] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2024] [Revised: 08/02/2024] [Accepted: 08/05/2024] [Indexed: 08/15/2024]
Abstract
Lipid synthesis and transport are essential for energy, production of cell membrane, and cell signaling. Acyl-CoA thioesterases (ACOTs) function to regulate intracellular levels of fatty acyl-CoAs through hydrolysis. Two members of this family, ACOT11 and ACOT12, contain steroidogenic acute regulatory related lipid transfer domains, which typically function as lipid transport or regulatory domains. This work reviews ACOT11 and ACOT12 structures and functions, and the potential role of the START domains in lipid transfer activity and the allosteric regulation of catalytic activity.
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Affiliation(s)
- Molly Little
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322, U.S.A
| | - Eric A Ortlund
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322, U.S.A
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2
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Mukherjee T, Subedi B, Khosla A, Begler EM, Stephens PM, Warner AL, Lerma-Reyes R, Thompson KA, Gunewardena S, Schrick K. The START domain mediates Arabidopsis GLABRA2 dimerization and turnover independently of homeodomain DNA binding. PLANT PHYSIOLOGY 2022; 190:2315-2334. [PMID: 35984304 PMCID: PMC9706451 DOI: 10.1093/plphys/kiac383] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Accepted: 06/09/2022] [Indexed: 05/08/2023]
Abstract
Class IV homeodomain leucine-zipper transcription factors (HD-Zip IV TFs) are key regulators of epidermal differentiation that are characterized by a DNA-binding HD in conjunction with a lipid-binding domain termed steroidogenic acute regulatory-related lipid transfer (START). Previous work established that the START domain of GLABRA2 (GL2), a HD-Zip IV member from Arabidopsis (Arabidopsis thaliana), is required for TF activity. Here, we addressed the functions and possible interactions of START and the HD in DNA binding, dimerization, and protein turnover. Deletion analysis of the HD and missense mutations of a conserved lysine (K146) resulted in phenotypic defects in leaf trichomes, root hairs, and seed mucilage, similar to those observed for START domain mutants, despite nuclear localization of the respective proteins. In vitro and in vivo experiments demonstrated that while HD mutations impair binding to target DNA, the START domain is dispensable for DNA binding. Vice versa, protein interaction assays revealed impaired GL2 dimerization for multiple alleles of START mutants, but not HD mutants. Using in vivo cycloheximide chase experiments, we provided evidence for the role of START, but not HD, in maintaining protein stability. This work advances our mechanistic understanding of HD-Zip TFs as multidomain regulators of epidermal development in plants.
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Affiliation(s)
- Thiya Mukherjee
- Division of Biology, Kansas State University, Manhattan, Kansas 66506, USA
- Molecular, Cellular and Developmental Biology, Kansas State University, Manhattan, Kansas 66506, USA
- Donald Danforth Plant Science Center, Olivette, Missouri 63132, USA
| | - Bibek Subedi
- Division of Biology, Kansas State University, Manhattan, Kansas 66506, USA
- Molecular, Cellular and Developmental Biology, Kansas State University, Manhattan, Kansas 66506, USA
| | - Aashima Khosla
- Division of Biology, Kansas State University, Manhattan, Kansas 66506, USA
- Molecular, Cellular and Developmental Biology, Kansas State University, Manhattan, Kansas 66506, USA
- Department of Botany and Plant Sciences, University of California, Riverside, California 92521, USA
| | - Erika M Begler
- Division of Biology, Kansas State University, Manhattan, Kansas 66506, USA
| | - Preston M Stephens
- Division of Biology, Kansas State University, Manhattan, Kansas 66506, USA
| | - Adara L Warner
- Division of Biology, Kansas State University, Manhattan, Kansas 66506, USA
| | - Ruben Lerma-Reyes
- Division of Biology, Kansas State University, Manhattan, Kansas 66506, USA
- Interdepartmental Genetics, Kansas State University, Manhattan, Kansas 66506, USA
| | - Kyle A Thompson
- Division of Biology, Kansas State University, Manhattan, Kansas 66506, USA
| | - Sumedha Gunewardena
- Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas 66160, USA
| | - Kathrin Schrick
- Division of Biology, Kansas State University, Manhattan, Kansas 66506, USA
- Molecular, Cellular and Developmental Biology, Kansas State University, Manhattan, Kansas 66506, USA
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3
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Sanchez-Solana B, Wang D, Qian X, Velayoudame P, Simanshu DK, Acharya JK, Lowy DR. The tumor suppressor activity of DLC1 requires the interaction of its START domain with Phosphatidylserine, PLCD1, and Caveolin-1. Mol Cancer 2021; 20:141. [PMID: 34727930 PMCID: PMC8561924 DOI: 10.1186/s12943-021-01439-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Accepted: 10/04/2021] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND DLC1, a tumor suppressor gene that is downregulated in many cancer types by genetic and nongenetic mechanisms, encodes a protein whose RhoGAP and scaffolding activities contribute to its tumor suppressor functions. The role of the DLC1 START (StAR-related lipid transfer; DLC1-START) domain, other than its binding to Caveolin-1, is poorly understood. In other START domains, a key function is that they bind lipids, but the putative lipid ligand for DLC1-START is unknown. METHODS Lipid overlay assays and Phosphatidylserine (PS)-pull down assays confirmed the binding of DLC1-START to PS. Co-immunoprecipitation studies demonstrated the interaction between DLC1-START and Phospholipase C delta 1 (PLCD1) or Caveolin-1, and the contribution of PS to those interactions. Rho-GTP, cell proliferation, cell migration, and/or anchorage-independent growth assays were used to investigate the contribution of PS and PLCD1, or the implications of TCGA cancer-associated DLC1-START mutants, to DLC1 functions. Co-immunoprecipitations and PS-pull down assays were used to investigate the molecular mechanisms underlying the impaired functions of DLC1-START mutants. A structural model of DLC1-START was also built to better understand the structural implications of the cancer-associated mutations in DLC1-START. RESULTS We identified PS as the lipid ligand for DLC1-START and determined that DLC1-START also binds PLCD1 protein in addition to Caveolin-1. PS binding contributes to the interaction of DLC1 with Caveolin-1 and with PLCD1. The importance of these activities for tumorigenesis is supported by our analysis of 7 cancer-associated DLC1-START mutants, each of which has reduced tumor suppressor function but retains wildtype RhoGAP activity. Our structural model of DLC1-START indicates the mutants perturb different elements within the structure, which is correlated with our experimental findings that the mutants are heterogenous with regard to the deficiency of their binding properties. Some have reduced PS binding, others reduced PLCD1 and Caveolin-1 binding, and others are deficient for all of these properties. CONCLUSION These observations highlight the importance of DLC1-START for the tumor suppressor function of DLC1 that is RhoGAP-independent. They also expand the versatility of START domains, as DLC1-START is the first found to bind PS, which promotes the binding to other proteins.
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Affiliation(s)
- Beatriz Sanchez-Solana
- Laboratory of Cellular Oncology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Dunrui Wang
- Laboratory of Cellular Oncology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Xiaolan Qian
- Laboratory of Cellular Oncology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Parthibane Velayoudame
- Cancer and Developmental Biology Laboratory, Center for Cancer Research, National Cancer Institute, NIH, Frederick, MD, 21701, USA
| | - Dhirendra K Simanshu
- NCI RAS Initiative, Cancer Research Technology Program, Frederick National Laboratory for Cancer Research, Leidos Biomedical Research, Frederick, MD, 21701, USA
| | - Jairaj K Acharya
- Cancer and Developmental Biology Laboratory, Center for Cancer Research, National Cancer Institute, NIH, Frederick, MD, 21701, USA
| | - Douglas R Lowy
- Laboratory of Cellular Oncology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD, 20892, USA.
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4
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Tillman MC, Imai N, Li Y, Khadka M, Okafor CD, Juneja P, Adhiyaman A, Hagen SJ, Cohen DE, Ortlund EA. Allosteric regulation of thioesterase superfamily member 1 by lipid sensor domain binding fatty acids and lysophosphatidylcholine. Proc Natl Acad Sci U S A 2020; 117:22080-22089. [PMID: 32820071 PMCID: PMC7486800 DOI: 10.1073/pnas.2003877117] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Nonshivering thermogenesis occurs in brown adipose tissue to generate heat in response to cold ambient temperatures. Thioesterase superfamily member 1 (Them1) is transcriptionally up-regulated in brown adipose tissue upon exposure to the cold and suppresses thermogenesis in order to conserve energy reserves. It hydrolyzes long-chain fatty acyl-CoAs that are derived from lipid droplets, preventing their use as fuel for thermogenesis. In addition to its enzymatic domains, Them1 contains a C-terminal StAR-related lipid transfer (START) domain with unknown ligand or function. By complementary biophysical approaches, we show that the START domain binds to long-chain fatty acids, products of Them1's enzymatic reaction, as well as lysophosphatidylcholine (LPC), lipids shown to activate thermogenesis in brown adipocytes. Certain fatty acids stabilize the START domain and allosterically enhance Them1 catalysis of acyl-CoA, whereas 18:1 LPC destabilizes and inhibits activity, which we verify in cell culture. Additionally, we demonstrate that the START domain functions to localize Them1 near lipid droplets. These findings define the role of the START domain as a lipid sensor that allosterically regulates Them1 activity and spatially localizes it in proximity to the lipid droplet.
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Affiliation(s)
- Matthew C Tillman
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322
| | - Norihiro Imai
- Joan and Sanford I. Weill Department of Medicine, Weill Cornell Medical College, New York, NY 10065
| | - Yue Li
- Department of Surgery, Beth Israel Deaconess Medical Center, Boston, MA 02215
| | - Manoj Khadka
- Emory Integrated Lipidomics Core, Emory University, Atlanta, GA 30322
| | - C Denise Okafor
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322
| | - Puneet Juneja
- Robert P. Apkarian Integrated Electron Microscopy Core, Emory University, Atlanta, GA 30322
| | - Akshitha Adhiyaman
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322
| | - Susan J Hagen
- Department of Surgery, Beth Israel Deaconess Medical Center, Boston, MA 02215
| | - David E Cohen
- Joan and Sanford I. Weill Department of Medicine, Weill Cornell Medical College, New York, NY 10065
| | - Eric A Ortlund
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322;
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5
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Tugaeva KV, Sluchanko NN. Steroidogenic Acute Regulatory Protein: Structure, Functioning, and Regulation. BIOCHEMISTRY (MOSCOW) 2019; 84:S233-S253. [PMID: 31213205 DOI: 10.1134/s0006297919140141] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Steroidogenesis takes place mainly in adrenal and gonadal cells that produce a variety of structurally similar hormones regulating numerous body functions. The rate-limiting stage of steroidogenesis is cholesterol delivery to the inner mitochondrial membrane, where it is converted by cytochrome P450scc into pregnenolone, a common precursor of all steroid hormones. The major role of supplying mitochondria with cholesterol belongs to steroidogenic acute regulatory protein (STARD1). STARD1, which is synthesized de novo as a precursor containing mitochondrial localization sequence and sterol-binding domain, significantly accelerates cholesterol transport and production of pregnenolone. Despite a tremendous interest in STARD1 fueled by its involvement in hereditary diseases and extensive efforts of numerous laboratories worldwide, many aspects of STARD1 structure, functioning, and regulation remain obscure and debatable. This review presents current concepts on the structure of STARD1 and other lipid transfer proteins, the role of STARD1 in steroidogenesis, and the mechanism of its functioning, as well as identifies the most controversial and least studied questions related to the activity of this protein.
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Affiliation(s)
- K V Tugaeva
- Bach Institute of Biochemistry, Federal Research Center of Biotechnology, Russian Academy of Sciences, Moscow, 119071, Russia. .,Lomonosov Moscow State University, Biological Faculty, Department of Biochemistry, Moscow, 119234, Russia
| | - N N Sluchanko
- Bach Institute of Biochemistry, Federal Research Center of Biotechnology, Russian Academy of Sciences, Moscow, 119071, Russia. .,Lomonosov Moscow State University, Biological Faculty, Department of Biophysics, Moscow, 119991, Russia
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6
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Horenkamp FA, Valverde DP, Nunnari J, Reinisch KM. Molecular basis for sterol transport by StART-like lipid transfer domains. EMBO J 2018; 37:embj.201798002. [PMID: 29467216 DOI: 10.15252/embj.201798002] [Citation(s) in RCA: 63] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Revised: 02/02/2018] [Accepted: 02/05/2018] [Indexed: 11/09/2022] Open
Abstract
Lipid transport proteins at membrane contact sites, where two organelles are closely apposed, play key roles in trafficking lipids between cellular compartments while distinct membrane compositions for each organelle are maintained. Understanding the mechanisms underlying non-vesicular lipid trafficking requires characterization of the lipid transporters residing at contact sites. Here, we show that the mammalian proteins in the lipid transfer proteins anchored at a membrane contact site (LAM) family, called GRAMD1a-c, transfer sterols with similar efficiency as the yeast orthologues, which have known roles in sterol transport. Moreover, we have determined the structure of a lipid transfer domain of the yeast LAM protein Ysp2p, both in its apo-bound and sterol-bound forms, at 2.0 Å resolution. It folds into a truncated version of the steroidogenic acute regulatory protein-related lipid transfer (StART) domain, resembling a lidded cup in overall shape. Ergosterol binds within the cup, with its 3-hydroxy group interacting with protein indirectly via a water network at the cup bottom. This ligand binding mode likely is conserved for the other LAM proteins and for StART domains transferring sterols.
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Affiliation(s)
- Florian A Horenkamp
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | - Diana P Valverde
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | - Jodi Nunnari
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, USA
| | - Karin M Reinisch
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
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7
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Tugaeva KV, Faletrov YV, Allakhverdiev ES, Shkumatov VM, Maksimov EG, Sluchanko NN. Effect of the NBD-group position on interaction of fluorescently-labeled cholesterol analogues with human steroidogenic acute regulatory protein STARD1. Biochem Biophys Res Commun 2018; 497:58-64. [DOI: 10.1016/j.bbrc.2018.02.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2018] [Accepted: 02/02/2018] [Indexed: 10/18/2022]
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8
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Sluchanko NN, Tugaeva KV, Maksimov EG. Solution structure of human steroidogenic acute regulatory protein STARD1 studied by small-angle X-ray scattering. Biochem Biophys Res Commun 2017; 489:445-450. [DOI: 10.1016/j.bbrc.2017.05.167] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Accepted: 05/28/2017] [Indexed: 12/11/2022]
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9
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The heat shock protein 60 promotes progesterone synthesis in mitochondria of JEG-3 cells. Reprod Biol 2017; 17:154-161. [DOI: 10.1016/j.repbio.2017.04.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Revised: 04/05/2017] [Accepted: 04/12/2017] [Indexed: 11/22/2022]
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10
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Khoury K, Barbar E, Ainmelk Y, Ouellet A, Lavigne P, LeHoux JG. Thirty-Eight-Year Follow-Up of Two Sibling Lipoid Congenital Adrenal Hyperplasia Patients Due to Homozygous Steroidogenic Acute Regulatory (STARD1) Protein Mutation. Molecular Structure and Modeling of the STARD1 L275P Mutation. Front Neurosci 2016; 10:527. [PMID: 27917104 PMCID: PMC5116571 DOI: 10.3389/fnins.2016.00527] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2016] [Accepted: 10/31/2016] [Indexed: 11/13/2022] Open
Abstract
Objective: Review the impact of StAR (STARD1) mutations on steroidogenesis and fertility in LCAH patients. Examine the endocrine mechanisms underlying the pathology of the disorder and the appropriate therapy for promoting fertility and pregnancies. Design: Published data in the literature and a detailed 38-year follow-up of two sibling LCAH patients. Molecular structure and modeling of the STARD1 L275P mutation. Setting: University hospital. Patients: Patient A (46,XY female phenotype) and patient B (46,XX female) with LCAH bearing the L275P mutation in STARD1. Interventions: Since early-age diagnosis, both patients underwent corticoid replacement therapy. Patient A received estrogen therapy at pubertal age. Clomiphene therapy was given to Patient B to induce ovulation. Pregnancies were protected with progesterone administration. Main Outcome Measures: Clinical and molecular assessment of adrenal and gonadal functions. Results: Both patients have classic manifestations of corticosteroid deficiency observed in LCAH. Time of onset and severity were different. Patient A developed into a female phenotype due to early and severe damage of Leydig cells. Patient B started a progressive pubertal development, menarche and regular non-ovulatory cycle. She was able to have successful pregnancies. Conclusions: Understanding the molecular structure and function of STARD1 in all steroidogenic tissues is the key for comprehending the heterogeneous clinical manifestations of LCAH, and the development of an appropriate strategy for the induction of ovulation and protecting pregnancies in this disease.
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Affiliation(s)
- Khalil Khoury
- Department of Pediatrics, Faculty of Medicine, University of Sherbrooke Sherbrooke, QC, Canada
| | - Elie Barbar
- Department of Biochemistry, Faculty of Medicine, University of Sherbrooke Sherbrooke, QC, Canada
| | - Youssef Ainmelk
- Department of Obstetrics and Gynecology, Faculty of Medicine, University of Sherbrooke Sherbrooke, QC, Canada
| | - Annie Ouellet
- Department of Obstetrics and Gynecology, Faculty of Medicine, University of Sherbrooke Sherbrooke, QC, Canada
| | - Pierre Lavigne
- Department of Biochemistry, Faculty of Medicine, University of Sherbrooke Sherbrooke, QC, Canada
| | - Jean-Guy LeHoux
- Department of Biochemistry, Faculty of Medicine, University of Sherbrooke Sherbrooke, QC, Canada
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11
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Elustondo P, Martin LA, Karten B. Mitochondrial cholesterol import. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1862:90-101. [PMID: 27565112 DOI: 10.1016/j.bbalip.2016.08.012] [Citation(s) in RCA: 92] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2016] [Revised: 08/15/2016] [Accepted: 08/19/2016] [Indexed: 02/06/2023]
Abstract
All animal subcellular membranes require cholesterol, which influences membrane fluidity and permeability, fission and fusion processes, and membrane protein function. The distribution of cholesterol among subcellular membranes is highly heterogeneous and the cholesterol content of each membrane must be carefully regulated. Compared to other subcellular membranes, mitochondrial membranes are cholesterol-poor, particularly the inner mitochondrial membrane (IMM). As a result, steroidogenesis can be controlled through the delivery of cholesterol to the IMM, where it is converted to pregnenolone. The low basal levels of cholesterol also make mitochondria sensitive to changes in cholesterol content, which can have a relatively large impact on the biophysical and functional characteristics of mitochondrial membranes. Increased mitochondrial cholesterol levels have been observed in diverse pathological conditions including cancer, steatohepatitis, Alzheimer disease and Niemann-Pick Type C1-deficiency, and are associated with increased oxidative stress, impaired oxidative phosphorylation, and changes in the susceptibility to apoptosis, among other alterations in mitochondrial function. Mitochondria are not included in the vesicular trafficking network; therefore, cholesterol transport to mitochondria is mostly achieved through the activity of lipid transfer proteins at membrane contact sites or by cytosolic, diffusible lipid transfer proteins. Here we will give an overview of the main mechanisms involved in mitochondrial cholesterol import, focusing on the steroidogenic acute regulatory protein StAR/STARD1 and other members of the StAR-related lipid transfer (START) domain protein family, and we will discuss how changes in mitochondrial cholesterol levels can arise and affect mitochondrial function. This article is part of a Special Issue entitled: Lipids of Mitochondria edited by Guenther Daum.
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Affiliation(s)
- Pia Elustondo
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Laura A Martin
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Barbara Karten
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS B3H 4R2, Canada.
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12
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Maxfield FR, Iaea DB, Pipalia NH. Role of STARD4 and NPC1 in intracellular sterol transport. Biochem Cell Biol 2016; 94:499-506. [PMID: 27421092 DOI: 10.1139/bcb-2015-0154] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Cholesterol plays an important role in determining the biophysical properties of membranes in mammalian cells, and the concentration of cholesterol in membranes is tightly regulated. Cholesterol moves among membrane organelles by a combination of vesicular and nonvesicular transport pathways, but the details of these transport pathways are not well understood. In this review, we discuss the mechanisms for nonvesicular sterol transport with an emphasis on the role of STARD4, a small, soluble, cytoplasmic sterol transport protein. STARD4 can rapidly equilibrate sterol between membranes, especially membranes with anionic lipid headgroups. We also discuss the sterol transport in late endosomes and lysosomes, which is mediated by a soluble protein, NPC2, and a membrane protein, NPC1. Homozygous mutations in these proteins lead to a lysosomal lipid storage disorder, Niemann-Pick disease type C. Many of the disease-causing mutations in NPC1 are associated with degradation of the mutant NPC1 proteins in the endoplasmic reticulum. Several histone deacetylase inhibitors have been found to rescue the premature degradation of the mutant NPC1 proteins, and one of these is now in a small clinical trial.
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Affiliation(s)
- Frederick R Maxfield
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, NY 10065, USA.,Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, NY 10065, USA
| | - David B Iaea
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, NY 10065, USA.,Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, NY 10065, USA
| | - Nina H Pipalia
- Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, NY 10065, USA.,Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, NY 10065, USA
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13
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Sluchanko NN, Tugaeva KV, Faletrov YV, Levitsky DI. High-yield soluble expression, purification and characterization of human steroidogenic acute regulatory protein (StAR) fused to a cleavable Maltose-Binding Protein (MBP). Protein Expr Purif 2015; 119:27-35. [PMID: 26555181 DOI: 10.1016/j.pep.2015.11.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Revised: 10/21/2015] [Accepted: 11/04/2015] [Indexed: 11/24/2022]
Abstract
Steroidogenic acute regulatory protein (StAR) is responsible for the rapid delivery of cholesterol to mitochondria where the lipid serves as a source for steroid hormones biosynthesis in adrenals and gonads. Despite many successful investigations, current understanding of the mechanism of StAR action is far from being completely clear. StAR was mostly obtained using denaturation/renaturation or in minor quantities in a soluble form at decreased temperatures that, presumably, limited the possibilities for its consequent detailed exploration. In our hands, existing StAR expression constructs could be bacterially expressed almost exclusively as insoluble forms, even upon decreased expression temperatures and in specific strains of Escherichia coli, and isolated protein tended to aggregate and was difficult to handle. To maximize the yield of soluble protein, optimized StAR sequence encompassing functional domain STARD1 (residues 66-285) was fused to the C-terminus of His-tagged Maltose-Binding Protein (MBP) with the possibility to cleave off the whole tag by 3C protease. The developed protocol of expression and purification comprising of a combination of subtractive immobilized metal affinity chromatography (IMAC) and size-exclusion chromatography allowed us to obtain up to 25 mg/1 L culture of completely soluble StAR protein, which was (i) homogenous according to SDS-PAGE, (ii) gave a single symmetrical peak on a gel-filtration, (iii) showed the characteristic CD spectrum and (iv) pH-dependent ability to bind a fluorescently-labeled cholesterol analogue. We conclude that our strategy provides fully soluble and native StAR protein which in future could be efficiently used for biotechnology and drug discovery aimed at modulation of steroids production.
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Affiliation(s)
- Nikolai N Sluchanko
- A.N. Bach Institute of Biochemistry, Research Center of Biotechnology of the Russian Academy of Sciences, Moscow, Russia.
| | - Kristina V Tugaeva
- A.N. Bach Institute of Biochemistry, Research Center of Biotechnology of the Russian Academy of Sciences, Moscow, Russia; Department of Biochemistry, School of Biology, Moscow State University, Moscow, Russia
| | - Yaroslav V Faletrov
- Research Institute for Physical Chemical Problems, Belarusian State University, Minsk, Belarus
| | - Dmitrii I Levitsky
- A.N. Bach Institute of Biochemistry, Research Center of Biotechnology of the Russian Academy of Sciences, Moscow, Russia; A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia
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14
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Abstract
The steroidogenic acute regulatory protein-related lipid transfer (START) domain family is defined by a conserved 210-amino acid sequence that folds into an α/β helix-grip structure. Members of this protein family bind a variety of ligands, including cholesterol, phospholipids, sphingolipids, and bile acids, with putative roles in nonvesicular lipid transport, metabolism, and cell signaling. Among the soluble START proteins, STARD4 is expressed in most tissues and has previously been shown to transfer sterol, but the molecular mechanisms of membrane interaction and sterol binding remain unclear. In this work, we use biochemical techniques to characterize regions of STARD4 and determine their role in membrane interaction and sterol binding. Our results show that STARD4 interacts with anionic membranes through a surface-exposed basic patch and that introducing a mutation (L124D) into the Omega-1 (Ω1) loop, which covers the sterol binding pocket, attenuates sterol transfer activity. To gain insight into the attenuating mechanism of the L124D mutation, we conducted structural and biophysical studies of wild-type and L124D STARD4. These studies show that the L124D mutation reduces the conformational flexibility of the protein, resulting in a diminished level of membrane interaction and sterol transfer. These studies also reveal that the C-terminal α-helix, and not the Ω1 loop, partitions into the membrane bilayer. On the basis of these observations, we propose a model of STARD4 membrane interaction and sterol binding and release that requires dynamic movement of both the Ω1 loop and membrane insertion of the C-terminal α-helix.
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Affiliation(s)
- David
B. Iaea
- Department
of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, New York 10065, United States,Weill Cornell Medical
College, Rockefeller University, and Memorial Sloan-Kettering Cancer
Center Tri-Institutional Chemical Biology Program, New York, New York 10065, United States
| | - Igor Dikiy
- Department
of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, New York 10065, United States
| | - Irene Kiburu
- Department
of Physiology and Biophysics, Weill Cornell
Medical College, 1300
York Avenue, New York, New
York 10065, United
States
| | - David Eliezer
- Department
of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, New York 10065, United States,Weill Cornell Medical
College, Rockefeller University, and Memorial Sloan-Kettering Cancer
Center Tri-Institutional Chemical Biology Program, New York, New York 10065, United States
| | - Frederick R. Maxfield
- Department
of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, New York 10065, United States,Weill Cornell Medical
College, Rockefeller University, and Memorial Sloan-Kettering Cancer
Center Tri-Institutional Chemical Biology Program, New York, New York 10065, United States,E-mail: . Telephone: (212) 746-6405. Fax: (212) 746-8875
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15
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Yüksel B, Kulle AE, Gürbüz F, Welzel M, Kotan D, Mengen E, Holterhus PM, Topaloğlu AK, Grötzinger J, Riepe FG. The novel mutation p.Trp147Arg of the steroidogenic acute regulatory protein causes classic lipoid congenital adrenal hyperplasia with adrenal insufficiency and 46,XY disorder of sex development. Horm Res Paediatr 2014; 80:163-9. [PMID: 23920000 DOI: 10.1159/000354086] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/20/2013] [Accepted: 06/25/2013] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The steroidogenic acute regulatory protein (StAR) is essential for steroidogenesis by mediating cholesterol transfer into mitochondria. Inactivating StAR mutations cause lipoid congenital adrenal hyperplasia. OBJECTIVE AND METHODS To identify causative mutations in a patient presenting with adrenal failure during early infancy. The objective was to study the functional and structural consequences of the novel StAR mutation p.Trp147Arg in a Turkish patient detected in compound heterozygosity with the p.Glu169Lys mutation. RESULTS Transient in vitro expression of the mutant proteins together with P450 side-chain cleavage enzyme, adrenodoxin, and adrenodoxin reductase yielded severely diminished cholesterol conversion of the p.Trp147Arg mutant. The previously described p.Glu169Lys mutant led to significantly lower cholesterol conversion than wild-type StAR protein. As derived from three-dimensional protein modeling, the residue W147 is stabilizing the C-terminal helix in a closed conformation hereby acting as gatekeeper of the ligand cavity of StAR. CONCLUSIONS The novel mutation p.Trp147Arg causes primary adrenal insufficiency and complete sex reversal in the 46,XY patient. Clinical disease, in vitro studies and three-dimensional protein modeling of the mutation p.Trp147Arg underscore the relevance of this highly conserved residue for StAR protein function.
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Affiliation(s)
- Bilgin Yüksel
- Division of Pediatric Endocrinology and Metabolism, Department of Pediatrics, Cukurova University, Balcali/Adana, Turkey
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16
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Camats N, Pandey AV, Fernández-Cancio M, Fernández JM, Ortega AM, Udhane S, Andaluz P, Audí L, Flück CE. STAR splicing mutations cause the severe phenotype of lipoid congenital adrenal hyperplasia: insights from a novel splice mutation and review of reported cases. Clin Endocrinol (Oxf) 2014; 80:191-9. [PMID: 23859637 DOI: 10.1111/cen.12293] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/16/2013] [Revised: 05/29/2013] [Accepted: 07/11/2013] [Indexed: 11/27/2022]
Abstract
OBJECTIVE The steroidogenic acute regulatory protein (StAR) transports cholesterol to the mitochondria for steroidogenesis. Loss of StAR function causes lipoid congenital adrenal hyperplasia (LCAH) which is characterized by impaired synthesis of adrenal and gonadal steroids causing adrenal insufficiency, 46,XY disorder of sex development (DSD) and failure of pubertal development. Partial loss of StAR activity may cause adrenal insufficiency only. PATIENT A newborn girl was admitted for mild dehydration, hyponatremia, hyperkalemia and hypoglycaemia and had normal external female genitalia without hyperpigmentation. Plasma cortisol, 17OH-progesterone, DHEA-S, androstendione and aldosterone were low, while ACTH and plasma renin activity were elevated, consistent with the diagnosis of primary adrenal insufficiency. Imaging showed normal adrenals, and cytogenetics revealed a 46,XX karyotype. She was treated with fluids, hydrocortisone and fludrocortisone. DESIGN, METHODS AND RESULTS Genetic studies revealed a novel homozygous STAR mutation in the 3' acceptor splice site of intron 4, c.466-1G>A (IVS4-1G>A). To test whether this mutation would affect splicing, we performed a minigene experiment with a plasmid construct containing wild-type or mutant StAR gDNA of exons-introns 4-6 in COS-1 cells. The splicing was assessed on total RNA using RT-PCR for STAR cDNAs. The mutant STAR minigene skipped exon 5 completely and changed the reading frame. Thus, it is predicted to produce an aberrant and shorter protein (p.V156GfsX19). Computational analysis revealed that this mutant protein lacks wild-type exons 5-7 which are essential for StAR-cholesterol interaction. CONCLUSIONS STAR c.466-1A skips exon 5 and causes a dramatic change in the C-terminal sequence of the protein, which is essential for StAR-cholesterol interaction. This splicing mutation is a loss-of-function mutation explaining the severe phenotype of our patient. Thus far, all reported splicing mutations of STAR cause a severe impairment of protein function and phenotype.
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Affiliation(s)
- Núria Camats
- Pediatric Endocrinology, Department of Pediatrics and Department of Clinical Research, University Children's Hospital Bern, Bern, Switzerland
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17
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Martinez N, Ribeiro EA, Leyrat C, Tarbouriech N, Ruigrok RWH, Jamin M. Structure of the C-terminal domain of lettuce necrotic yellows virus phosphoprotein. J Virol 2013; 87:9569-78. [PMID: 23785215 PMCID: PMC3754093 DOI: 10.1128/jvi.00999-13] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2013] [Accepted: 06/14/2013] [Indexed: 12/26/2022] Open
Abstract
Lettuce necrotic yellows virus (LNYV) is a prototype of the plant-adapted cytorhabdoviruses. Through a meta-prediction of disorder, we localized a folded C-terminal domain in the amino acid sequence of its phosphoprotein. This domain consists of an autonomous folding unit that is monomeric in solution. Its structure, solved by X-ray crystallography, reveals a lollipop-shaped structure comprising five helices. The structure is different from that of the corresponding domains of other Rhabdoviridae, Filoviridae, and Paramyxovirinae; only the overall topology of the polypeptide chain seems to be conserved, suggesting that this domain evolved under weak selective pressure and varied in size by the acquisition or loss of functional modules.
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Affiliation(s)
- Nicolas Martinez
- Université Grenoble Alpes, UVHCI, Grenoble, France
- CNRS, UVHCI, Grenoble, France
- Unit for Virus Host-Cell Interactions, Université Grenoble Alpes-EMBL-CNRS, Grenoble, France
- Institut Laue Langevin, Grenoble, France
| | - Euripedes A. Ribeiro
- Université Grenoble Alpes, UVHCI, Grenoble, France
- CNRS, UVHCI, Grenoble, France
- Unit for Virus Host-Cell Interactions, Université Grenoble Alpes-EMBL-CNRS, Grenoble, France
| | - Cédric Leyrat
- Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, United Kingdom
| | - Nicolas Tarbouriech
- Université Grenoble Alpes, UVHCI, Grenoble, France
- CNRS, UVHCI, Grenoble, France
- Unit for Virus Host-Cell Interactions, Université Grenoble Alpes-EMBL-CNRS, Grenoble, France
| | - Rob W. H. Ruigrok
- Université Grenoble Alpes, UVHCI, Grenoble, France
- CNRS, UVHCI, Grenoble, France
- Unit for Virus Host-Cell Interactions, Université Grenoble Alpes-EMBL-CNRS, Grenoble, France
| | - Marc Jamin
- Université Grenoble Alpes, UVHCI, Grenoble, France
- CNRS, UVHCI, Grenoble, France
- Unit for Virus Host-Cell Interactions, Université Grenoble Alpes-EMBL-CNRS, Grenoble, France
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Thorsell AG, Lee WH, Persson C, Siponen MI, Nilsson M, Busam RD, Kotenyova T, Schüler H, Lehtiö L. Comparative structural analysis of lipid binding START domains. PLoS One 2011; 6:e19521. [PMID: 21738568 PMCID: PMC3127847 DOI: 10.1371/journal.pone.0019521] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2011] [Accepted: 03/31/2011] [Indexed: 11/24/2022] Open
Abstract
Background Steroidogenic acute regulatory (StAR) protein related lipid transfer (START) domains are small globular modules that form a cavity where lipids and lipid hormones bind. These domains can transport ligands to facilitate lipid exchange between biological membranes, and they have been postulated to modulate the activity of other domains of the protein in response to ligand binding. More than a dozen human genes encode START domains, and several of them are implicated in a disease. Principal Findings We report crystal structures of the human STARD1, STARD5, STARD13 and STARD14 lipid transfer domains. These represent four of the six functional classes of START domains. Significance Sequence alignments based on these and previously reported crystal structures define the structural determinants of human START domains, both those related to structural framework and those involved in ligand specificity. Enhanced version This article can also be viewed as an enhanced version in which the text of the article is integrated with interactive 3D representations and animated transitions. Please note that a web plugin is required to access this enhanced functionality. Instructions for the installation and use of the web plugin are available in Text S1.
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Affiliation(s)
- Ann-Gerd Thorsell
- Department of Medical Biochemistry and Biophysics, Structural Genomics Consortium, Karolinska Institutet, Stockholm, Sweden
| | - Wen Hwa Lee
- Structural Genomics Consortium, University of Oxford, Headington, Oxford, United Kingdom
| | - Camilla Persson
- Department of Medical Biochemistry and Biophysics, Structural Genomics Consortium, Karolinska Institutet, Stockholm, Sweden
| | - Marina I. Siponen
- Department of Medical Biochemistry and Biophysics, Structural Genomics Consortium, Karolinska Institutet, Stockholm, Sweden
| | - Martina Nilsson
- Department of Medical Biochemistry and Biophysics, Structural Genomics Consortium, Karolinska Institutet, Stockholm, Sweden
| | - Robert D. Busam
- Department of Medical Biochemistry and Biophysics, Structural Genomics Consortium, Karolinska Institutet, Stockholm, Sweden
| | - Tetyana Kotenyova
- Department of Medical Biochemistry and Biophysics, Structural Genomics Consortium, Karolinska Institutet, Stockholm, Sweden
| | - Herwig Schüler
- Department of Medical Biochemistry and Biophysics, Structural Genomics Consortium, Karolinska Institutet, Stockholm, Sweden
- * E-mail: (LL); (HS)
| | - Lari Lehtiö
- Department of Medical Biochemistry and Biophysics, Structural Genomics Consortium, Karolinska Institutet, Stockholm, Sweden
- Department of Biosciences, Pharmaceutical Sciences, Åbo Akademi University, Turku, Finland
- * E-mail: (LL); (HS)
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Evans AN, Nunez BS. Regulation of mRNAs encoding the steroidogenic acute regulatory protein and cholesterol side-chain cleavage enzyme in the elasmobranch interrenal gland. Gen Comp Endocrinol 2010; 168:121-32. [PMID: 20417210 DOI: 10.1016/j.ygcen.2010.04.018] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/05/2009] [Revised: 04/11/2010] [Accepted: 04/20/2010] [Indexed: 11/30/2022]
Abstract
The rate-limiting and regulated step in steroidogenesis, the conversion of cholesterol to pregnenolone, is facilitated by the steroidogenic acute regulatory protein (StAR) and cytochrome P450 cholesterol side-chain cleavage (P450scc). We have isolated cDNAs encoding StAR and P450scc from the Atlantic stingray, Dasyatis sabina, and characterized the steroidogenic activity of the encoded proteins using a heterologous expression system. Green monkey kidney (COS-1) cells cotransfected with D. sabina StAR and human P450scc/adrenodoxin reductase/adrenodoxin fusion (F2) constructs produced significantly more pregnenolone than cells transfected with the F2 construct alone. COS-1 cells transfected with a modified F2 construct (F2DS) in which human P450scc is replaced by D. sabina P450scc had higher rates than cells transfected with D. sabina P450scc alone. In other vertebrates, the stress peptide adrenocorticotropic hormone (ACTH) elicits its effects on corticosteroidogenesis in part through regulation of StAR and P450scc mRNAs. In vitro incubation of D. sabina interrenal tissue with porcine ACTH significantly increased intracellular cAMP and corticosteroid production. As demonstrated by quantitative PCR, ACTH also induced significant increases in mRNA abundance of both StAR and P450scc. Our results suggest that, as in higher vertebrates, chronic ACTH-induced glucocorticoid synthesis in elasmobranchs is mediated by regulation of primary steroidogenic mRNAs. This study is the first to demonstrate steroidogenic activity of an elasmobranch P450scc protein and express a composite elasmobranch steroidogenic pathway in a heterologous cell line. Also, the regulation of StAR and P450scc mRNAs has not previously been demonstrated in elasmobranch fishes.
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Affiliation(s)
- Andrew N Evans
- The University of Texas Marine Science Institute, 750 Channel View Drive, Port Aransas, TX 78373, USA.
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Bens S, Mohn A, Yüksel B, Kulle AE, Michalek M, Chiarelli F, Nuri Ozbek M, Leuschner I, Grötzinger J, Holterhus PM, Riepe FG. Congenital lipoid adrenal hyperplasia: functional characterization of three novel mutations in the STAR gene. J Clin Endocrinol Metab 2010; 95:1301-8. [PMID: 20080861 DOI: 10.1210/jc.2009-1176] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
CONTEXT The steroidogenic acute regulatory protein (StAR) has been shown to be essential for steroidogenesis by mediating cholesterol transfer into mitochondria. Inactivating StAR mutations cause the typical clinical picture of congenital lipoid adrenal hyperplasia. OBJECTIVE The objective of the investigation was to study the functional and structural consequences of three novel StAR mutations (p.N148K in an Italian patient; p.P129fs and p.Q128R in a Turkish patient). METHODS AND RESULTS Transient in vitro expression of the mutant proteins together with P450 side-chain cleavage enzyme, adrenodoxin, and adrenodoxin reductase yielded severely diminished cholesterol conversion of the p.N148K mutant, the combined p.P129fs and p.Q128R mutant, and the p.P129fs mutant by itself. The p.Q128R mutant led to a higher cholesterol conversion than the wild-type StAR protein. As derived from three-dimensional protein modeling, the residue N148 is lining the ligand cavity of StAR. A positively charged lysine residue at position 148 disturbs the hydrophobic cluster formed by the alpha4-helix and the sterol binding pocket. The frame shift mutation p.P129fs truncates the StAR protein. Residue p.Q128 is situated at the surface of the molecule and is not part of any functionally characterized region of the protein. CONCLUSION The mutations p.N148K and p.P129fs cause adrenal insufficiency in both cases and lead to a disorder of sex development with complete sex reversal in the 46, XY case. The mutation p.Q128R, which is not relevant for the patient's phenotype, is the first reported variant showing a gain of function. We speculate that the substitution of hydrophilic glutamine with basic arginine at the surface of the molecule may accelerate cholesterol transfer.
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Affiliation(s)
- Susanne Bens
- Division of Pediatric Endocrinology, Department of Pediatrics, University Hospital Schleswig- Holstein, Schwanenweg 20, D-24105 Kiel, Germany
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21
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Lavigne P, Najmanivich R, Lehoux JG. Mammalian StAR-related lipid transfer (START) domains with specificity for cholesterol: structural conservation and mechanism of reversible binding. Subcell Biochem 2010; 51:425-437. [PMID: 20213553 DOI: 10.1007/978-90-481-8622-8_15] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The StAR-related lipid transfer (START) domain is an evolutionary conserved protein module of approximately 210 amino acids. There are 15 mammalian proteins that possess a START domain. Whereas the functions and specific ligands are being elucidated, 5 of them have already been shown to bind specifically cholesterol. The most intensively studied member of this subclass is the steroidogenic acute regulatory protein (StAR) or STARD1. While its role in steroid hormone production has been demonstrated, much less is understood about how its START domain specifically recognizes cholesterol and how it releases it to be transferred inside the mitochondria of steroidogenic cell of the gonads and adrenal cortex. A major obstacle that is slowing down progress in this area is the lack of knowledge of the 3D structures of the START domain of StAR in both its free and complexed forms. However, 3D models of the START domain of StAR and mechanisms of binding have been proposed. In addition biophysical studies aimed at validating the models and mechanism have been published. What's more, the crystal structures of the free forms of 3 START domains (STARD3, STARD4 and STARD5) known to specifically bind cholesterol have been elucidated so far. In this chapter, we will review and critically summarize existing data in order to provide the most current view and status of our understanding of the structure and reversible cholesterol binding mechanism of START domains.
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Affiliation(s)
- Pierre Lavigne
- Département de Pharmacologie, Institut de Pharmacologie, Université de Sherbrooke, Sherbrooke, QC, Canada.
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22
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Barbar E, Lehoux JG, Lavigne P. Toward the NMR structure of StAR. Mol Cell Endocrinol 2009; 300:89-93. [PMID: 19138724 DOI: 10.1016/j.mce.2008.12.007] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/14/2008] [Revised: 12/02/2008] [Accepted: 12/02/2008] [Indexed: 11/21/2022]
Abstract
The steroidogenic acute regulatory (StAR) protein plays a crucial role in steroidogenesis, as it accelerates the transport of cholesterol to the inner mitochondrial membrane where the cytochrome P450scc enzyme is located. Mutations in the StAR gene can lead to lipoid congenital adrenal hyperplasia (LCAH), a disease that is fatal if not treated with hormone replacement therapy. Solving the structure of StAR is an important aspect of understanding LCAH. Point mutations or truncations in the StAR gene produce a partial to non-functional protein that hinders the StAR-induced delivery of cholesterol to the mitochondria during an acute hormonal stimulation of steroidogenic cells. So far, homology modeling, structure-based thermodynamics and biophysical studies have allowed us to propose the existence of an open state of StAR where the C-terminal alpha-helix 4 undergoes partial unfolding. This may act as a gating mechanism to the cholesterol binding site. Once bound, cholesterol leads to the stabilization and the refolding of alpha-helix 4, and eventually to the interaction with an import complex at the surface of the mitochondria. Though the current homology models have proven useful in understanding StAR function, only the full determination of the 3D structure of the apo- and holo-states will further validate this two-state model. In this context, we have used solution-state nuclear magnetic resonance (NMR) and obtained high-resolution (1)H-(15)N-HSQC spectra of StAR in its apo- and holo-states at physiological pH. Both spectra displayed well-dispersed resonances. However, key differences are observed on the spectra which indicate that both states have stable but slightly different tertiary structures. In conjunction with the binding/activity assays and biophysical methods, this original NMR data constitutes another structural step into the validation of the two-state model and the three-dimensional structure of StAR.
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Affiliation(s)
- Elie Barbar
- Département de Biochimie, Faculté de médecine et des sciences de la santé, Université de Sherbrooke, Sherbrooke, Québec, Canada, J1H 5N4
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Barbar E, Lavigne P, Lehoux JG. Validation of the mechanism of cholesterol binding by StAR using short molecular dynamics simulations. J Steroid Biochem Mol Biol 2009; 113:92-7. [PMID: 19095060 DOI: 10.1016/j.jsbmb.2008.11.008] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/05/2008] [Accepted: 11/21/2008] [Indexed: 11/30/2022]
Abstract
We previously proposed an original two-state cholesterol binding mechanism by StAR, in which the C-terminal alpha-helix of StAR gates the access of cholesterol to its binding site cavity. This cavity, which can accommodate one cholesterol molecule, was proposed to promote the reversible unfolding of the C-terminal alpha-helix and allow for the entry and dissociation of cholesterol. In our molecular model of the cholesterol-StAR complex, the hydrophobic moiety of cholesterol interacts with hydrophobic amino acid side-chains located in the C-terminal alpha-helix and at the bottom of the cavity. In this study, we present a structural in silico analysis of StAR. Molecular dynamics simulations showed that point mutations of Phe(267), Leu(271) or Leu(275) at the alpha-helix 4 increased the gyration radius (more flexibility) of the protein's structure, whereas the salt bridge double mutant E169M/R188M showed a decrease in flexibility (more compactness). Also, in the latter case, an interaction between Met(169) and Phe(267) disrupted the hydrophobic cavity, rendering it impervious to ligand binding. These obtained results are in agreement with previous in vitro experiments, and provide further validation of the two-state binding mode of action.
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Affiliation(s)
- Elie Barbar
- Département de Biochimie, Faculté de médecine et des sciences de la santé, Université de Sherbrooke, Sherbrooke, Québec, Canada J1H 5N4
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