1
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Le NTK, Kang EJ, Park JH, Kang K. Catechol-Amyloid Interactions. Chembiochem 2023; 24:e202300628. [PMID: 37850717 DOI: 10.1002/cbic.202300628] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2023] [Revised: 10/17/2023] [Accepted: 10/18/2023] [Indexed: 10/19/2023]
Abstract
This review introduces multifaceted mutual interactions between molecules containing a catechol moiety and aggregation-prone proteins. The complex relationships between these two molecular species have previously been elucidated primarily in a unidirectional manner, as demonstrated in cases involving the development of catechol-based inhibitors for amyloid aggregation and the elucidation of the role of functional amyloid fibers in melanin biosynthesis. This review aims to consolidate scattered clues pertaining to catechol-based amyloid inhibitors, functional amyloid scaffold of melanin biosynthesis, and chemically designed peptide fibers for providing chemical insights into the role of the local three-dimensional orientation of functional groups in manifesting such interactions. These orientations may play crucial, yet undiscovered, roles in various supramolecular structures.
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Affiliation(s)
- Nghia T K Le
- Department of Applied Chemistry, Kyung Hee University, Yongin, Gyeonggi, 17104, South Korea
| | - Eun Joo Kang
- Department of Applied Chemistry, Kyung Hee University, Yongin, Gyeonggi, 17104, South Korea
| | - Ji Hun Park
- Department of Science Education, Ewha Womans University, Seoul, 03760, South Korea
| | - Kyungtae Kang
- Department of Applied Chemistry, Kyung Hee University, Yongin, Gyeonggi, 17104, South Korea
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2
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Buchanan JA, Varghese NR, Johnston CL, Sunde M. Functional Amyloids: Where Supramolecular Amyloid Assembly Controls Biological Activity or Generates New Functionality. J Mol Biol 2023; 435:167919. [PMID: 37330295 DOI: 10.1016/j.jmb.2022.167919] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2022] [Revised: 12/05/2022] [Accepted: 12/05/2022] [Indexed: 06/19/2023]
Abstract
Functional amyloids are a rapidly expanding class of fibrillar protein structures, with a core cross-β scaffold, where novel and advantageous biological function is generated by the assembly of the amyloid. The growing number of amyloid structures determined at high resolution reveal how this supramolecular template both accommodates a wide variety of amino acid sequences and also imposes selectivity on the assembly process. The amyloid fibril can no longer be considered a generic aggregate, even when associated with disease and loss of function. In functional amyloids the polymeric β-sheet rich structure provides multiple different examples of unique control mechanisms and structures that are finely tuned to deliver assembly or disassembly in response to physiological or environmental cues. Here we review the range of mechanisms at play in natural, functional amyloids, where tight control of amyloidogenicity is achieved by environmental triggers of conformational change, proteolytic generation of amyloidogenic fragments, or heteromeric seeding and amyloid fibril stability. In the amyloid fibril form, activity can be regulated by pH, ligand binding and higher order protofilament or fibril architectures that impact the arrangement of associated domains and amyloid stability. The growing understanding of the molecular basis for the control of structure and functionality delivered by natural amyloids in nearly all life forms should inform the development of therapies for amyloid-associated diseases and guide the design of innovative biomaterials.
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Affiliation(s)
- Jessica A Buchanan
- School of Medical Sciences and Sydney Nano, The University of Sydney, NSW 2006, Australia.
| | - Nikhil R Varghese
- School of Medical Sciences and Sydney Nano, The University of Sydney, NSW 2006, Australia.
| | - Caitlin L Johnston
- School of Medical Sciences and Sydney Nano, The University of Sydney, NSW 2006, Australia.
| | - Margaret Sunde
- School of Medical Sciences and Sydney Nano, The University of Sydney, NSW 2006, Australia.
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3
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Dean DN, Lee JC. Monitoring Kinetics of pH-Dependent Aggregation and Disaggregation of the Pmel17 Repeat Domain. Methods Mol Biol 2023; 2551:79-93. [PMID: 36310198 DOI: 10.1007/978-1-0716-2597-2_7] [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] [Indexed: 06/16/2023]
Abstract
The premelanosomal protein (Pmel17) is a human functional amyloid that promotes pigmentation by serving as a scaffold for melanin polymerization. This occurs within the melanosome, where Pmel17 is first proteolyzed into smaller domain(s) that are responsible for fibril formation. Our work has shown that the Pmel17 repeat domain (RPT, residues 315-444) forms amyloid fibrils in vitro under acidic conditions similar to those found in melanosomes. Mechanistically, this is driven by the protonation of acidic residues, resulting in charge neutralization and subsequent aggregation. Interestingly, the deprotonation of acidic residues leads to rapid disaggregation, highlighting a reversible mechanism of fibril formation and dissolution thus far only observed for functional amyloid proteins. In this chapter, we describe how to monitor pH-dependent RPT aggregation and disaggregation using extrinsic thioflavin-T and intrinsic tryptophan fluorescence, respectively. These methods can also be adapted more broadly to investigate the reversibility of other amyloid systems, both functional and pathogenic.
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Affiliation(s)
- Dexter N Dean
- The Laboratory of Protein Conformation and Dynamics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Jennifer C Lee
- The Laboratory of Protein Conformation and Dynamics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA.
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4
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Quiñones-Ruiz T, Rosario-Alomar MF, Shanmugasundaram M, Ali MM, Lednev IK. Spontaneous Refolding of Amyloid Fibrils from One Polymorph to Another Caused by Changes in Environmental Hydrophobicity. Biochemistry 2022; 61:1456-1464. [PMID: 35786852 DOI: 10.1021/acs.biochem.2c00143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Here, we report a new phenomenon in which lysozyme fibrils formed in a solution of acetic acid spontaneously refold to a different polymorph through a disassembled intermediate upon the removal of acetic acid. The structural changes were revealed and characterized by deep-UV resonance Raman spectroscopy, nonresonance Raman spectroscopy, intrinsic tryptophan fluorescence spectroscopy, and atomic force microscopy. A PPII-like structure with highly solvent-exposed tryptophan residues predominates the intermediate aggregates before refolding to polymorph II fibrils. Furthermore, the disulfide (SS) bonds undergo significant rearrangements upon the removal of acetic acid from the lysozyme fibril environment. The main SS bond conformation changes from gauche-gauche-trans in polymorph I to gauche-gauche-gauche in polymorph II. Changing the hydrophobicity of the fibril environment was concluded to be the decisive factor causing the spontaneous refolding of lysozyme fibrils from one polymorph to another upon the removal of acetic acid. Potential biological implications of the discovered phenomenon are discussed.
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Affiliation(s)
- Tatiana Quiñones-Ruiz
- Department of Chemistry, University at Albany, SUNY, Albany, New York 12222, United States
| | | | | | - Muhammad M Ali
- Department of Chemistry, University at Albany, SUNY, Albany, New York 12222, United States
| | - Igor K Lednev
- Department of Chemistry, University at Albany, SUNY, Albany, New York 12222, United States
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5
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Betschart MU, Sarem M, Shastri VP, Lüdeke S. Reversible, β-sheet-dependent self-assembly of the phosphoprotein phosvitin is controlled by the concentration and valency of cations. Phys Chem Chem Phys 2022; 24:11791-11800. [PMID: 35506877 DOI: 10.1039/d1cp05493g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The hyperphosphorylated protein phosvitin (PV) undergoes a pH-dependent transition between PII- and β-sheet secondary structures, a process deemed crucial for its role in the promotion of biogenic apatite formation. The transition occurs surprisingly slowly (minutes to hours). This is consistent with a slow aggregation process involving ionic interactions of charged groups on the protein surface. Herein, we determined the associated transition pK values and time constants through matrix least-squares (MLS) global fitting of a series of pH- and time-dependent circular dichroism (CD) spectra recorded in the presence of different mono-, bi- and trivalent cations. Supporting our results with dynamic light scattering data, we clearly identified a close correlation of β-sheet transition and the formation of small aggregates at low pH. This process is inhibited in the presence of all tested cations with the strongest effects for trivalent cations (Fe3+ and Al3+). In the presence of Ca2+ and Mg2+, larger higher-order particles are formed from PV in the β-sheet conformation, as identified from the interpretation of differential scattering observed in the CD spectra. Our observations are consistent with the existence of a multi-step equilibrium between aggregated and non-aggregated species of PV. The equilibrium is highly sensitive to the environment pH and salt concentration with exceptional behavior in the presence of divalent cations such as Ca2+ and Mg2+.
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Affiliation(s)
- Martin U Betschart
- Institut für Pharmazeutische Wissenschaften, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany
| | - Melika Sarem
- Institute for Macromolecular Chemistry, Albert-Ludwigs-Universität Freiburg, Stefan-Meier-Str. 31, 79104 Freiburg, Germany.,BIOSS - Centre for Biological Signalling Studies, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany
| | - V Prasad Shastri
- Institute for Macromolecular Chemistry, Albert-Ludwigs-Universität Freiburg, Stefan-Meier-Str. 31, 79104 Freiburg, Germany.,BIOSS - Centre for Biological Signalling Studies, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany
| | - Steffen Lüdeke
- Institut für Pharmazeutische Wissenschaften, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany.,Institut für Pharmazeutische und Biomedizinische Wissenschaften (IPBW), Johannes Gutenberg-Universität Mainz, Staudingerweg 5, 55128 Mainz, Germany.
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6
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Dogra P, Arya S, Singh AK, Datta A, Mukhopadhyay S. Conformational and Solvation Dynamics of an Amyloidogenic Intrinsically Disordered Domain of a Melanosomal Protein. J Phys Chem B 2022; 126:443-452. [PMID: 34986640 DOI: 10.1021/acs.jpcb.1c09304] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The conformational plasticity of intrinsically disordered proteins (IDPs) allows them to adopt a range of conformational states that can be important for their biological functions. The driving force for the conformational preference of an IDP emanates from an intricate interplay between chain-chain and chain-solvent interactions. Using ultrafast femtosecond and picosecond time-resolved fluorescence measurements, we characterized the conformational and solvation dynamics around the N- and C-terminal segments of a disordered repeat domain of a melanosomal protein Pmel17 that forms functional amyloid responsible for melanin biosynthesis. Our time-resolved fluorescence anisotropy results revealed slight compaction and slower rotational dynamics around the amyloidogenic C-terminal segment when compared to the proline-rich N-terminal segment of the repeat domain. The compaction of the C-terminal region was also associated with the restrained mobility of hydration water as indicated by our solvation dynamics measurements. Our findings indicate that sequence-dependent chain-solvent interactions govern both the conformational and solvation dynamics that are crucial in directing the conversion of a highly dynamic IDP into an ordered amyloid assembly. Such an interplay of amino acid composition-dependent conformational and solvation dynamics might have important physicochemical consequences in specific water-protein, ion-protein, and protein-protein interactions involved in amyloid formation and phase transitions.
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Affiliation(s)
| | | | - Avinash K Singh
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, Maharashtra 400076, India
| | - Anindya Datta
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, Maharashtra 400076, India
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7
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Pedrioli G, Barberis M, Magrin C, Morone D, Piovesana E, Senesi G, Sola M, Papin S, Paganetti P. Tau Seeds in Extracellular Vesicles Induce Tau Accumulation in Degradative Organelles of Cells. DNA Cell Biol 2021; 40:1185-1199. [PMID: 34379990 DOI: 10.1089/dna.2021.0485] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Clinical progression of tauopathies may result from transcellular propagation of pathogenic Tau seeds with the possible involvement of extracellular vesicles (EVs) as transport vectors. We established a cell model for investigating EV delivery of proteins, since the mechanism regulating EV cargo delivery to recipient cells is poorly understood. In our cell model, EVs are readily internalized and accumulate in degradative organelles (DOs). We then show for the first time that in this acidic compartment, profibrillogenic Tau delivered by EVs interacts with Tau expressed by the recipient cells and cause its accumulation by a process that involves the participation of autophagy. Thus, the degradative compartment of cells may represent the subcellular site initiating a cascade of events resulting in early hallmarks of tauopathies. These are characterized by seeded Tau accumulation, pathology-associated epitopes, DO stress, and cytotoxicity. The involvement of autophagy to this process and the relative accessibility of the degradative pathway for extracellular agents, support possible modes of intervention to slow down the progression of neurodegeneration.
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Affiliation(s)
- Giona Pedrioli
- Neurodegeneration Research Group, Laboratory for Biomedical Neurosciences, Neurocenter of Southern Switzerland, Ente Ospedaliero Cantonale, Lugano, Switzerland.,Program of the Science Research, Biozentrum, University of Basel, Basel, Switzerland
| | - Marialuisa Barberis
- Neurodegeneration Research Group, Laboratory for Biomedical Neurosciences, Neurocenter of Southern Switzerland, Ente Ospedaliero Cantonale, Lugano, Switzerland
| | - Claudia Magrin
- Neurodegeneration Research Group, Laboratory for Biomedical Neurosciences, Neurocenter of Southern Switzerland, Ente Ospedaliero Cantonale, Lugano, Switzerland.,Faculty of Biomedical Sciences, Università della Svizzera italiana (USI), Lugano, Switzerland
| | - Diego Morone
- Faculty of Biomedical Sciences, Institute for Research in Biomedicine, Università della Svizzera italiana (USI), Lugano, Switzerland
| | - Ester Piovesana
- Neurodegeneration Research Group, Laboratory for Biomedical Neurosciences, Neurocenter of Southern Switzerland, Ente Ospedaliero Cantonale, Lugano, Switzerland.,Faculty of Biomedical Sciences, Università della Svizzera italiana (USI), Lugano, Switzerland
| | - Giorgia Senesi
- Neurodegeneration Research Group, Laboratory for Biomedical Neurosciences, Neurocenter of Southern Switzerland, Ente Ospedaliero Cantonale, Lugano, Switzerland.,Scienze Biomediche Biomolecolari, Università degli Studi di Pavia, Pavia, Italy
| | - Martina Sola
- Neurodegeneration Research Group, Laboratory for Biomedical Neurosciences, Neurocenter of Southern Switzerland, Ente Ospedaliero Cantonale, Lugano, Switzerland.,Faculty of Biomedical Sciences, Università della Svizzera italiana (USI), Lugano, Switzerland
| | - Stéphanie Papin
- Neurodegeneration Research Group, Laboratory for Biomedical Neurosciences, Neurocenter of Southern Switzerland, Ente Ospedaliero Cantonale, Lugano, Switzerland
| | - Paolo Paganetti
- Neurodegeneration Research Group, Laboratory for Biomedical Neurosciences, Neurocenter of Southern Switzerland, Ente Ospedaliero Cantonale, Lugano, Switzerland.,Faculty of Biomedical Sciences, Università della Svizzera italiana (USI), Lugano, Switzerland
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8
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Dean DN, Lee JC. Purification and characterization of an amyloidogenic repeat domain from the functional amyloid Pmel17. Protein Expr Purif 2021; 187:105944. [PMID: 34293440 DOI: 10.1016/j.pep.2021.105944] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2021] [Revised: 07/16/2021] [Accepted: 07/17/2021] [Indexed: 01/15/2023]
Abstract
The pre-melanosomal protein (Pmel17) is a human functional amyloid that supports melanin biosynthesis within melanocytes. This occurs in the melanosome, a membrane-bound organelle with an acidic intraluminal pH. The repeat region of Pmel17 (RPT, residues 315-444) has been previously shown to form amyloid aggregates under acidic melanosomal conditions, but not under neutral cytosolic conditions, when expressed and purified using a C-terminal hexa-histidine tag (RPT-His). Given the importance of protonation states in RPT-His aggregation, we questioned whether the histidine tag influenced the pH-dependent behavior. In this report, we generated a tagless RPT by inserting a tobacco etch virus (TEV) protease recognition sequence (ENLYGQ(G/S)) immediately upstream of a native glycine residue at position 312 in Pmel17. After purification of the fusion construct using a histidine tag, cleavage with TEV protease generated a fully native RPT (nRPT) spanning resides 312-444. We characterized the aggregation of nRPT, which formed amyloid fibrils under acidic conditions (pH ≤ 6) but not at neutral pH. Characterizing the morphologies of nRPT aggregates using transmission electron microscopy revealed a pH-dependent maturation from short, curved structures at pH 4 to paired, rod-like fibrils at pH 6. This was accompanied by a secondary structural transition from mixed random coil/β-sheet at pH 4 to canonical β-sheet at pH 6. We also show that pre-formed nRPT fibrils undergo disaggregation upon dilution into pH 7 buffer. More broadly, this strategy can be utilized to generate native amyloidogenic domains from larger proteins by utilizing intrinsic N-terminal glycine or serine residues.
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Affiliation(s)
- Dexter N Dean
- Laboratory of Protein Conformation and Dynamics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, United States
| | - Jennifer C Lee
- Laboratory of Protein Conformation and Dynamics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, United States.
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9
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Dean DN, Lee JC. Linking Parkinson's Disease and Melanoma: Interplay Between α-Synuclein and Pmel17 Amyloid Formation. Mov Disord 2021; 36:1489-1498. [PMID: 34021920 DOI: 10.1002/mds.28655] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Revised: 04/22/2021] [Accepted: 04/30/2021] [Indexed: 12/13/2022] Open
Abstract
Parkinson's disease (PD) is a neurodegenerative disorder associated with the death of dopaminergic neurons within the substantia nigra of the brain. Melanoma is a cancer of melanocytes, pigmented cells that give rise to skin tone, hair, and eye color. Although these two diseases fundamentally differ, with PD leading to cell degeneration and melanoma leading to cell proliferation, epidemiological evidence has revealed a reciprocal relationship where patients with PD are more susceptible to melanoma and patients with melanoma are more susceptible to PD. The hallmark pathology observed in PD brains is intracellular inclusions, of which the primary component is proteinaceous α-synuclein (α-syn) amyloid fibrils. α-Syn also has been detected in cultured melanoma cells and tissues derived from patients with melanoma, where an inverse correlation exists between α-syn expression and pigmentation. Although this has led to the prevailing hypothesis that α-syn inhibits enzymes involved in melanin biosynthesis, we recently reported an alternative hypothesis in which α-syn interacts with and modulates the aggregation of Pmel17, a functional amyloid that serves as a scaffold for melanin biosynthesis. In this perspective, we review the literature describing the epidemiological and molecular connections between PD and melanoma, presenting both the prevailing hypothesis and our amyloid-centric hypothesis. We offer our views of the essential questions that remain unanswered to motivate future investigations. Understanding the behavior of α-syn in melanoma could not only provide novel approaches for treating melanoma but also could reveal insights into the role of α-syn in PD. © 2021 International Parkinson and Movement Disorder Society.
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Affiliation(s)
- Dexter N Dean
- Laboratory of Protein Conformation and Dynamics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Jennifer C Lee
- Laboratory of Protein Conformation and Dynamics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
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10
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Identification of critical amino acid residues in the regulatory N-terminal domain of PMEL. Sci Rep 2021; 11:7730. [PMID: 33833328 PMCID: PMC8032716 DOI: 10.1038/s41598-021-87259-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2020] [Accepted: 03/26/2021] [Indexed: 01/22/2023] Open
Abstract
The pigment cell-specific protein PMEL forms a functional amyloid matrix in melanosomes onto which the pigment melanin is deposited. The amyloid core consists of a short proteolytic fragment, which we have termed the core-amyloid fragment (CAF) and perhaps additional parts of the protein, such as the PKD domain. A highly O-glycosylated repeat (RPT) domain also derived from PMEL proteolysis associates with the amyloid and is necessary to establish the sheet-like morphology of the assemblies. Excluded from the aggregate is the regulatory N-terminus, which nevertheless must be linked in cis to the CAF in order to drive amyloid formation. The domain is then likely cleaved away immediately before, during, or immediately after the incorporation of a new CAF subunit into the nascent amyloid. We had previously identified a 21 amino acid long region, which mediates the regulatory activity of the N-terminus towards the CAF. However, many mutations in the respective segment caused misfolding and/or blocked PMEL export from the endoplasmic reticulum, leaving their phenotype hard to interpret. Here, we employ a saturating mutagenesis approach targeting the motif at single amino acid resolution. Our results confirm the critical nature of the PMEL N-terminal region and identify several residues essential for PMEL amyloidogenesis.
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11
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Mugnai ML, Thirumalai D. Molecular Transfer Model for pH Effects on Intrinsically Disordered Proteins: Theory and Applications. J Chem Theory Comput 2021; 17:1944-1954. [PMID: 33566618 DOI: 10.1021/acs.jctc.0c01316] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We present a theoretical method to study how changes in pH shape the heterogeneous conformational ensemble explored by intrinsically disordered proteins (IDPs). The theory is developed in the context of coarse-grained models, which enable a fast, accurate, and extensive exploration of conformational space at a given protonation state. In order to account for pH effects, we generalize the molecular transfer model (MTM), in which conformations are re-weighted using the transfer free energy, which is the free energy necessary for bringing to equilibrium in a new environment a "frozen" conformation of the system. Using the semi-grand ensemble, we derive an exact expression of the transfer free energy, which amounts to the appropriate summation over all the protonation states. Because the exact result is computationally too demanding to be useful for large polyelectrolytes or IDPs, we introduce a mean-field (MF) approximation of the transfer free energy. Using a lattice model, we compare the exact and MF results for the transfer free energy and a variety of observables associated with the model IDP. We find that the precise location of the charged groups (the sequence), and not merely the net charge, determines the structural properties. We demonstrate that some of the limitations previously noted for MF theory in the context of globular proteins are mitigated when disordered polymers are studied. The excellent agreement between the exact and MF results poises us to use the method presented here as a computational tool to study the properties of IDPs and other biological systems as a function of pH.
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Affiliation(s)
- Mauro Lorenzo Mugnai
- Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
| | - D Thirumalai
- Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
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12
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Mukhopadhyay S. The Dynamism of Intrinsically Disordered Proteins: Binding-Induced Folding, Amyloid Formation, and Phase Separation. J Phys Chem B 2020; 124:11541-11560. [PMID: 33108190 DOI: 10.1021/acs.jpcb.0c07598] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Intrinsically disordered proteins (IDPs) or natively unfolded proteins do not undergo autonomous folding into a well-defined 3-D structure and challenge the conventional structure-function paradigm. They are involved in a multitude of critical physiological functions by adopting various structural states via order-to-disorder transitions or by maintaining their disordered characteristics in functional complexes. In recent times, there has been a burgeoning interest in the investigation of intriguing behavior of IDPs using highly multidisciplinary and complementary approaches due to the pivotal role of this unique class of protein chameleons in physiology and disease. Over the past decade or so, our laboratory has been actively investigating the unique physicochemical properties of this class of highly dynamic, flexible, rapidly interconverting proteins. We have utilized a diverse array of existing and emerging tools involving steady-state and time-resolved fluorescence, Raman spectroscopy, circular dichroism, light scattering, fluorescence microscopy, and atomic force microscopy coupled with site-directed mutagenesis and other biochemical and biophysical tools to study a variety of interesting and important aspects of IDPs. In this Feature Article, I describe our work on the conformational characteristics, solvation dynamics, binding-induced folding, amyloid formation, and liquid-liquid phase separation of a number of amyloidogenic IDPs. A series of these studies described here captures the role of conformational plasticity and dynamics in directing binding, folding, assembly, aggregation, and phase transitions implicated in physiology and pathology.
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Affiliation(s)
- Samrat Mukhopadhyay
- Centre for Protein Science, Design and Engineering, Department of Biological Sciences, and Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER), Mohali, India
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13
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Hofmeister Ions Modulate the Autocatalytic Amyloidogenesis of an Intrinsically Disordered Functional Amyloid Domain via Unusual Biphasic Kinetics. J Mol Biol 2020; 432:6173-6186. [PMID: 33068637 DOI: 10.1016/j.jmb.2020.10.015] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2020] [Revised: 10/01/2020] [Accepted: 10/11/2020] [Indexed: 02/06/2023]
Abstract
Hofmeister ions are thought to play fundamentally important roles in protein solubility, folding, stability, and function. Salt ions profoundly influence the course of protein misfolding, aggregation, and amyloid formation associated with devastating human diseases. However, the molecular origin of the salt-effect in protein aggregation remains elusive. Here, we report an unusual biphasic amyloidogenesis of a pH-responsive, intrinsically disordered, oligopeptide repeat domain of a melanosomal protein, Pmel17, that regulates the amyloid-assisted melanin synthesis in mammals via functional amyloid formation. We demonstrate that a symphony of molecular events involving charge-peptide interactions and hydration, in conjunction with secondary phenomena, critically governs the course of this biphasic amyloid assembly. We show that at mildly acidic pH, typical of melanosomes, highly amyloidogenic oligomeric units assemble into metastable, dendritic, fractal networks following the forward Hofmeister series. However, the subsequent condensation of fractal networks via conformational maturation into amyloid fibrils follows an inverse Hofmeister series due to fragmentation events coupled with secondary nucleation processes. Our results indicate that ions exert a strong influence on the aggregation kinetics as well as on the nanoscale morphology and also modulate the autocatalytic amplification processes during amyloid assembly via an intriguing dual Hofmeister effect. This unique interplay of molecular drivers will be of prime importance in delineating the aggregation pathways of a multitude of intrinsically disordered proteins involved in physiology and disease.
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14
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Choi RH, Kim HT. Analysis of oligomeric complexes of the amyloid-forming FYLLYY peptide by collision-induced dissociation with electrospray ionization mass spectrometry. EUROPEAN JOURNAL OF MASS SPECTROMETRY (CHICHESTER, ENGLAND) 2020; 26:361-368. [PMID: 32915641 DOI: 10.1177/1469066720958373] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The monomeric and oligomeric structures of the "FYLLYY" β2 microglobulin (β2m) active sequence, formed in (DMSO/CH3CN) solution, were investigated using electrospray ionization (ESI) mass spectrometry (MS) and tandem mass spectrometry (MS/MS). Dissociation of dimer and trimer ions was investigated by tandem mass spectrometry using collision induced dissociation (CID). The covalent bond fragmentation patterns were observed in the 21+ and 32+ MS/MS spectra (21+ = [dimer+H]1+ and 32+ = [trimer + 2H]2+). A π-π stacking geometry for the FYLLYY 21+ complex and partial parallel β-sheet geometry for the 32+ complex are proposed to be stable structures. The observed covalent bond fragment ions in the MS/MS spectra of the 32+ complex are considered to have originated from the partial parallel β-sheet moiety. The FYLLYY → AALLGY (or FYLLAA) substituted sequence was also investigated by CID-MS/MS. Our MS/MS analysis suggests that the π-π stacking interaction structures are important in dimer binding rather than the structures of a complete parallel or anti-parallel β-sheet 21+ complex.
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Affiliation(s)
- Ryu Ho Choi
- Department of Applied Chemistry, Kumoh National Institute of Technology, Gumi, Republic of Korea
| | - Ho-Tae Kim
- Department of Applied Chemistry, Kumoh National Institute of Technology, Gumi, Republic of Korea
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15
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Dean DN, Lee JC. Modulating functional amyloid formation via alternative splicing of the premelanosomal protein PMEL17. J Biol Chem 2020; 295:7544-7553. [PMID: 32277052 PMCID: PMC7247297 DOI: 10.1074/jbc.ra120.013012] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2020] [Revised: 04/07/2020] [Indexed: 12/30/2022] Open
Abstract
The premelanosomal protein (PMEL17) forms functional amyloid fibrils involved in melanin biosynthesis. Multiple PMEL17 isoforms are produced, two of which arise from excision of a cryptic intron within the amyloid-forming repeat (RPT) domain, leading to long (lRPT) and short (sRPT) isoforms with 10 and 7 imperfect repeats, respectively. Both lRPT and sRPT isoforms undergo similar pH-dependent mechanisms of amyloid formation and fibril dissolution. Here, using human PMEL17, we tested the hypothesis that the minor, but more aggregation-prone, sRPT facilitates amyloid formation of lRPT. We observed that cross-seeding by sRPT fibrils accelerates the rate of lRPT aggregation, resulting in propagation of an sRPT-like twisted fibril morphology, unlike the rodlike structure that lRPT normally adopts. This templating was specific, as the reversed reaction inhibited sRPT fibril formation. Despite displaying ultrastructural differences, self- and cross-seeded lRPT fibrils had a similar β-sheet structured core, revealed by Raman spectroscopy, limited-proteolysis, and fibril disaggregation experiments, suggesting the fibril twist is modulated by N-terminal residues outside the amyloid core. Interestingly, bioinformatics analysis of PMEL17 homologs from other mammals uncovered that long and short RPT isoforms are conserved among members of this phylogenetic group. Collectively, our results indicate that the short isoform of RPT serves as a "nucleator" of PMEL17 functional amyloid formation, mirroring how bacterial functional amyloids assemble during biofilm formation. Whereas bacteria regulate amyloid assembly by using individual genes within the same operon, we propose that the modulation of functional amyloid formation in higher organisms can be accomplished through alternative splicing.
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Affiliation(s)
- Dexter N Dean
- Laboratory of Protein Conformation and Dynamics, Biochemistry and Biophysics Center, NHLBI, National Institutes of Health, Bethesda, Maryland 20892
| | - Jennifer C Lee
- Laboratory of Protein Conformation and Dynamics, Biochemistry and Biophysics Center, NHLBI, National Institutes of Health, Bethesda, Maryland 20892.
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16
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Histidine-Lacked Aβ(1–16) Peptides: pH-Dependent Conformational Changes in Metal Ion Binding. Int J Pept Res Ther 2020. [DOI: 10.1007/s10989-020-10048-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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17
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Dogra P, Joshi A, Majumdar A, Mukhopadhyay S. Intermolecular Charge-Transfer Modulates Liquid–Liquid Phase Separation and Liquid-to-Solid Maturation of an Intrinsically Disordered pH-Responsive Domain. J Am Chem Soc 2019; 141:20380-20389. [DOI: 10.1021/jacs.9b10892] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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18
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Intramelanocytic Acidification Plays a Role in the Antimelanogenic and Antioxidative Properties of Vitamin C and Its Derivatives. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2019; 2019:2084805. [PMID: 31214276 PMCID: PMC6535878 DOI: 10.1155/2019/2084805] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/30/2018] [Accepted: 03/31/2019] [Indexed: 12/31/2022]
Abstract
Although vitamin C (VC, L-ascorbic acid) has been widely used as a skin lightening agent for a long time, the mechanism by which it inhibits melanogenesis remains poorly understood. It is well-documented that the intramelanocytic pH is an important factor in regulating tyrosinase function and melanosome maturation. The activity of tyrosinase, the rate-limiting enzyme required for melanin synthesis, is generally minimal in an acidic environment. Given that VC is an acidic compound, we might speculate that the intracellular acidification of melanocytes induced by VC likely reduces melanin content through the suppression of tyrosinase activity. The results of this study reveal that treatment of melanocytes with VC or its derivatives, magnesium ascorbyl phosphate (MAP) and 3-O-ethyl-L-ascorbic acid (AAE), resulted in significant decreases in the tyrosinase activity and melanin content and in the levels of intracellular reactive oxygen species (ROS), indicating that VC and its derivatives possess antimelanogenic and antioxidative activities. Western blotting analysis indicated that VC, MAP, and AAE exert their antimelanogenic activity by inhibiting the tyrosinase activity rather than by downregulating the expression of melanogenic proteins such as tyrosinase, premelanosome protein 17 (Pmel17) and microphthalmia-associated transcription factor (MITF). Further, we found that the reduced tyrosinase activity of melanocytes treated with VC or its derivatives could be reactivated following intracellular neutralization induced by ammonium chloride (NH4Cl) or concanamycin A (Con A). Finally, we examined the expression of sodium-dependent VC transporter-2 (SVCT-2) using western blotting and qPCR, which revealed that there was a significant increase in the expression of SVCT-2 in melanocytes following treatment with VC. VC-mediated intracellular acidification was neutralized by phloretin (a putative SVCT-2 inhibitor) in a dose-dependent manner. Taken together, these data show that VC and its derivatives suppress tyrosinase activity through cytoplasmic acidification that potentially results from enhanced VC transmembrane transport via the VC transporter SVCT-2.
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19
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Graham M, Tzika AC, Mitchell SM, Liu X, Leonhardt RM. Repeat domain-associated O-glycans govern PMEL fibrillar sheet architecture. Sci Rep 2019; 9:6101. [PMID: 30988362 PMCID: PMC6465243 DOI: 10.1038/s41598-019-42571-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2018] [Accepted: 02/06/2019] [Indexed: 12/20/2022] Open
Abstract
PMEL is a pigment cell-specific protein that forms a functional amyloid matrix in melanosomes. The matrix consists of well-separated fibrillar sheets on which the pigment melanin is deposited. Using electron tomography, we demonstrate that this sheet architecture is governed by the PMEL repeat (RPT) domain, which associates with the amyloid as an accessory proteolytic fragment. Thus, the RPT domain is dispensable for amyloid formation as such but shapes the morphology of the matrix, probably in order to maximize the surface area available for pigment adsorption. Although the primary amino acid sequence of the RPT domain differs vastly among various vertebrates, we show that it is a functionally conserved, interchangeable module. RPT domains of all species are predicted to be very highly O-glycosylated, which is likely the common defining feature of this domain. O-glycosylation is indeed essential for RPT domain function and the establishment of the PMEL sheet architecture. Thus, O-glycosylation, not amino acid sequence, appears to be the major factor governing the characteristic PMEL amyloid morphology.
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Affiliation(s)
- Morven Graham
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT, 06519, USA
| | - Athanasia C Tzika
- Department of Genetics & Evolution, Laboratory of Artificial & Natural Evolution (LANE), Sciences III Building, 1211, Geneva, 4, Switzerland
| | - Susan M Mitchell
- Department of Immunobiology, Yale University School of Medicine, 300 Cedar Street, New Haven, CT, 06519, USA
| | - Xinran Liu
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT, 06519, USA
| | - Ralf M Leonhardt
- Department of Immunobiology, Yale University School of Medicine, 300 Cedar Street, New Haven, CT, 06519, USA.
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20
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Dean DN, Lee JC. pH-Dependent fibril maturation of a Pmel17 repeat domain isoform revealed by tryptophan fluorescence. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2019; 1867:961-969. [PMID: 30716507 DOI: 10.1016/j.bbapap.2019.01.012] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2018] [Revised: 01/24/2019] [Accepted: 01/28/2019] [Indexed: 11/19/2022]
Abstract
The pre-melanosomal protein (Pmel17) aggregates within melanosomes to form functional amyloid fibrils that facilitate melanin polymerization. The repeat domain (RPT) of Pmel17 fibrillates under strict acidic melanosomal pH. Alternative splicing results in a shortened repeat domain (sRPT), which also forms amyloid fibrils. Here, we explored the effects of pH and protein concentration on sRPT aggregation by monitoring the intrinsic fluorescence of the sole tryptophan at position 381 (381W). 381W emission properties revealed changes of local environment polarity for sRPT fibrils formed at different pH. At pH 4, fibrils formed rapidly with no lag phase. A high 381W intensity was observed with a slight blue shift (10 nm). These fibrils underwent further structural rearrangements at intermediate pH (5-6), mirroring that of melanosome maturation, which initiates at pH 4 and increases to near neutral pH. In contrast, typical sigmoidal kinetics were observed at pH 6 with slower rates and 381W exhibited quenched emission. Interestingly, biphasic kinetics were observed at pH 5 in a protein concentration-dependent manner. A large 381W blue shift (23 nm) was measured, indicating a more hydrophobic environment for fibrils made at pH 5. Consistent with 381W fluorescence, Raman spectroscopy revealed molecular level perturbations in sRPT fibrils that were not evident from circular dichroism, transmission electron microscopy, or limited proteolysis analysis. Finally, sRPT fibrils did not form at pH ≥7 and preformed fibrils rapidly disaggregated under these solution conditions. Collectively, this work yields mechanistic insights into pH-dependent sRPT aggregation in the context of melanosome maturation.
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Affiliation(s)
- Dexter N Dean
- Laboratory of Protein Conformation and Dynamics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, United States
| | - Jennifer C Lee
- Laboratory of Protein Conformation and Dynamics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, United States.
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21
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Pedersen JN, Jiang Z, Christiansen G, Lee JC, Pedersen JS, Otzen DE. Lysophospholipids induce fibrillation of the repeat domain of Pmel17 through intermediate core-shell structures. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2018; 1867:519-528. [PMID: 30471451 DOI: 10.1016/j.bbapap.2018.11.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2018] [Revised: 11/02/2018] [Accepted: 11/17/2018] [Indexed: 11/26/2022]
Abstract
Lipids often play an important role in the initial steps of fibrillation. The melanosomal protein Pmel17 forms amyloid in vivo and contains a highly amyloidogenic Repeat domain (RPT), important for melanin biosynthesis. RPT fibrillation is influenced by two lysolipids, the anionic lysophosphatidylglycerol (LPG) and zwitterionic lysophosphatidylcholine (LPC), both present in vivo at elevated concentrations in melanosomes, organelles in which Pmel17 aggregate. Here we investigate the interaction of RPT with both LPG and LPC using small-angle X-ray scattering (SAXS), isothermal titration calorimetry (ITC), electron microscopy, fluorescence and circular dichroism (CD) spectroscopy. Under non-shaking conditions, both lipids promote fibrillation but this is driven by different interactions with RPT. Each RPT binds >40 LPG molecules but only weak interactions are seen with LPC. Above LPG's criticial micelle concentration (cmc), LPG and RPT form connected micelles where RPT binds to the surface as beads on a string with core-shell structures. Binding to LPG only induces α-helical structure well above the cmc, while LPC has no measurable effect on the protein structure. While low (but still super-cmc) concentrations of LPG strongly promote aggregation, at higher LPG concentrations (10 mM), only ~ one RPT binds per micelle, inhibiting amyloid formation. ITC and SAXS reveal some interactions between the zwitterionic lipid LPC and RPT below the cmc but little above the cmc. Nevertheless, LPC only promotes aggregation above the cmc and this process is not inhibited by high LPC concentrations, suggesting that monomers and micelles cooperate to influence amyloid formation.
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Affiliation(s)
- Jannik Nedergaard Pedersen
- Interdisciplinary Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus, Denmark
| | - Zhiping Jiang
- Laboratory of Protein Conformation and Dynamics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-8013, USA
| | - Gunna Christiansen
- Department of Biomedicine, Aarhus University, Wilhelm Meyers Allé 4, DK-8000 Aarhus, Denmark
| | - Jennifer C Lee
- Laboratory of Protein Conformation and Dynamics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-8013, USA
| | - Jan Skov Pedersen
- Interdisciplinary Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus, Denmark.
| | - Daniel E Otzen
- Interdisciplinary Nanoscience Center (iNANO), Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus, Denmark.
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22
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Abstract
Structural differences in pathological and functional amyloid fibrils have been investigated by Raman microspectroscopy. Second-derivative analyses of amide-I and amide-III bands distinguish parallel in-register β-sheets from a β-solenoid. Further, spatially resolved Raman spectra reveal molecular heterogeneity in amyloid structures.
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Affiliation(s)
- Jessica D Flynn
- Laboratory of Protein Conformation and Dynamics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
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23
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Why Study Functional Amyloids? Lessons from the Repeat Domain of Pmel17. J Mol Biol 2018; 430:3696-3706. [PMID: 29886018 DOI: 10.1016/j.jmb.2018.06.011] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2018] [Revised: 05/18/2018] [Accepted: 06/04/2018] [Indexed: 11/24/2022]
Abstract
One of the current challenges facing biomedical researchers is the need to develop new approaches in preventing amyloid formation that is associated with disease. While amyloid is generally considered detrimental to the cell, examples of amyloids that maintain a benign nature and serve a specific function exist. Here, we review our work on the repeat domain (RPT) of the functional amyloid Pmel17. Specifically, the RPT domain contributes in generating amyloid fibrils in melanosomes upon which melanin biosynthesis occurs. Amyloid formation of RPT was shown to be pH sensitive, aggregating only under acidic conditions associated with melanosomal pH. Furthermore, preformed fibrils rapidly dissolved at neutral pH to generate benign monomeric species. From a biological perspective, this unique reversible aggregation/disaggregation is a safeguard against an event of releasing RPT fibrils in the cytosol, resulting in rapid fibril unfolding and circumventing cytotoxicity. Understanding how melanosomes preserve a safe environment will address vital questions that remain unanswered with pathological amyloids.
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24
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Auer S. Simple Model of the Effect of Solution Conditions on the Nucleation of Amyloid Fibrils. J Phys Chem B 2017; 121:8893-8901. [DOI: 10.1021/acs.jpcb.7b05400] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Stefan Auer
- School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K
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25
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Moriarty GM, Olson MP, Atieh TB, Janowska MK, Khare SD, Baum J. A pH-dependent switch promotes β-synuclein fibril formation via glutamate residues. J Biol Chem 2017; 292:16368-16379. [PMID: 28710275 DOI: 10.1074/jbc.m117.780528] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2017] [Revised: 07/11/2017] [Indexed: 01/10/2023] Open
Abstract
α-Synuclein (αS) is the primary protein associated with Parkinson's disease, and it undergoes aggregation from its intrinsically disordered monomeric form to a cross-β fibrillar form. The closely related homolog β-synuclein (βS) is essentially fibril-resistant under cytoplasmic physiological conditions. Toxic gain-of-function by βS has been linked to dysfunction, but the aggregation behavior of βS under altered pH is not well-understood. In this work, we compare fibril formation of αS and βS at pH 7.3 and mildly acidic pH 5.8, and we demonstrate that pH serves as an on/off switch for βS fibrillation. Using αS/βS domain-swapped chimera constructs and single residue substitutions in βS, we localized the switch to acidic residues in the N-terminal and non-amyloid component domains of βS. Computational models of βS fibril structures indicate that key glutamate residues (Glu-31 and Glu-61) in these domains may be sites of pH-sensitive interactions, and variants E31A and E61A show dramatically altered pH sensitivity for fibril formation supporting the importance of these charged side chains in fibril formation of βS. Our results demonstrate that relatively small changes in pH, which occur frequently in the cytoplasm and in secretory pathways, may induce the formation of βS fibrils and suggest a complex role for βS in synuclein cellular homeostasis and Parkinson's disease.
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Affiliation(s)
- Gina M Moriarty
- From the Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey 08854
| | - Michael P Olson
- From the Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey 08854
| | - Tamr B Atieh
- From the Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey 08854
| | - Maria K Janowska
- From the Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey 08854
| | - Sagar D Khare
- From the Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey 08854
| | - Jean Baum
- From the Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey 08854
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26
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McGlinchey RP, Lee JC. Reversing the amyloid trend: Mechanism of fibril assembly and dissolution of the repeat domain from a human functional amyloid. Isr J Chem 2017; 57:613-621. [PMID: 28993712 PMCID: PMC5630176 DOI: 10.1002/ijch.201600080] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Amyloids are traditionally observed in the context of disease. However, there is growing momentum that these structures can serve a beneficial role where the amyloid carries out a specific function. These so called 'functional amyloids' have all the structural hallmarks of disease-associated amyloids, raising the question as to what differentiates a well-behaved benign amyloid from a lethally destructive one. Here, we review our work on the repeat domain (RPT) from Pmel17, an important functional amyloid involved in melanin biosynthesis. Particularly, we focused our attention on the unique reversible aggregation-disaggregation process of RPT that is controlled strictly by solution pH. This pH dependence of RPT amyloid formation functions as a switch to control fibril assembly and maintains the benign nature that is associated with functional amyloids.
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Affiliation(s)
- Ryan P. McGlinchey
- Laboratory of Protein Conformation and Dynamics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, U.S.A
| | - Jennifer C. Lee
- Laboratory of Protein Conformation and Dynamics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, U.S.A
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27
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Louros NN, Iconomidou VA. Identification of an amyloid fibril forming segment of human Pmel17 repeat domain (RPT domain). Biopolymers 2017; 106:133-9. [PMID: 26394553 DOI: 10.1002/bip.22746] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2015] [Revised: 08/24/2015] [Accepted: 09/18/2015] [Indexed: 12/20/2022]
Abstract
Pmel17 is the major component of functional amyloid fibrils that have an important role during pigment deposition. Pmel17 polymerization is promoted within the mildly acidic conditions of melanosomes, organelles located in pigment-specific cells. A repeat domain (RPT domain) of Pmel17, rich in glutamic acid residues has been extensively associated with the formation of the fibrous matrix. Here, we examine the RPT domain of human Pmel17 in order to provide information on this mechanism. Specifically, we have identified an aggregation-prone peptide segment ((405) VSIVVLSGT(413) ), close to the C-terminal part of the RPT domain. Experimental results utilizing electron microscopy, X-ray fiber diffraction, Congo red staining and ATR FT-IR spectroscopy indicate that this peptide segment self-assembles forming fibrils with evident amyloidogenic properties. Conclusively, our results demonstrate that the (405) VSIVVLSGT(413) peptide segment possibly has an essential role in RPT domain fibrillogenesis.
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Affiliation(s)
- Nikolaos N Louros
- Department of Cell Biology and Biophysics, Faculty of Biology, University of Athens, Panepistimiopolis, Athens, 157 01, Greece
| | - Vassiliki A Iconomidou
- Department of Cell Biology and Biophysics, Faculty of Biology, University of Athens, Panepistimiopolis, Athens, 157 01, Greece
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28
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Dogra P, Bhattacharya M, Mukhopadhyay S. pH-Responsive Mechanistic Switch Regulates the Formation of Dendritic and Fibrillar Nanostructures of a Functional Amyloid. J Phys Chem B 2017; 121:412-419. [DOI: 10.1021/acs.jpcb.6b11281] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Priyanka Dogra
- Centre
for Protein Science Design and Engineering, ‡Department of Biological Sciences, and §Department of
Chemical Sciences, Indian Institute of Science Education and Research (IISER) Mohali, SAS Nagar 140306, Punjab, India
| | - Mily Bhattacharya
- Centre
for Protein Science Design and Engineering, ‡Department of Biological Sciences, and §Department of
Chemical Sciences, Indian Institute of Science Education and Research (IISER) Mohali, SAS Nagar 140306, Punjab, India
| | - Samrat Mukhopadhyay
- Centre
for Protein Science Design and Engineering, ‡Department of Biological Sciences, and §Department of
Chemical Sciences, Indian Institute of Science Education and Research (IISER) Mohali, SAS Nagar 140306, Punjab, India
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29
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Louros NN, Baltoumas FA, Hamodrakas SJ, Iconomidou VA. A β-solenoid model of the Pmel17 repeat domain: insights to the formation of functional amyloid fibrils. J Comput Aided Mol Des 2016; 30:153-64. [PMID: 26754844 DOI: 10.1007/s10822-015-9892-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2015] [Accepted: 12/21/2015] [Indexed: 10/22/2022]
Abstract
Pmel17 is a multidomain protein involved in biosynthesis of melanin. This process is facilitated by the formation of Pmel17 amyloid fibrils that serve as a scaffold, important for pigment deposition in melanosomes. A specific luminal domain of human Pmel17, containing 10 tandem imperfect repeats, designated as repeat domain (RPT), forms amyloid fibrils in a pH-controlled mechanism in vitro and has been proposed to be essential for the formation of the fibrillar matrix. Currently, no three-dimensional structure has been resolved for the RPT domain of Pmel17. Here, we examine the structure of the RPT domain by performing sequence threading. The resulting model was subjected to energy minimization and validated through extensive molecular dynamics simulations. Structural analysis indicated that the RPT model exhibits several distinct properties of β-solenoid structures, which have been proposed to be polymerizing components of amyloid fibrils. The derived model is stabilized by an extensive network of hydrogen bonds generated by stacking of highly conserved polar residues of the RPT domain. Furthermore, the key role of invariant glutamate residues is proposed, supporting a pH-dependent mechanism for RPT domain assembly. Conclusively, our work attempts to provide structural insights into the RPT domain structure and to elucidate its contribution to Pmel17 amyloid fibril formation.
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Affiliation(s)
- Nikolaos N Louros
- Department of Cell Biology and Biophysics, Faculty of Biology, University of Athens, Panepistimiopolis, 157 01, Athens, Greece
| | - Fotis A Baltoumas
- Department of Cell Biology and Biophysics, Faculty of Biology, University of Athens, Panepistimiopolis, 157 01, Athens, Greece
| | - Stavros J Hamodrakas
- Department of Cell Biology and Biophysics, Faculty of Biology, University of Athens, Panepistimiopolis, 157 01, Athens, Greece
| | - Vassiliki A Iconomidou
- Department of Cell Biology and Biophysics, Faculty of Biology, University of Athens, Panepistimiopolis, 157 01, Athens, Greece.
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30
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vandenAkker CC, Deckert-Gaudig T, Schleeger M, Velikov KP, Deckert V, Bonn M, Koenderink GH. Nanoscale Heterogeneity of the Molecular Structure of Individual hIAPP Amyloid Fibrils Revealed with Tip-Enhanced Raman Spectroscopy. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2015; 11:4131-4139. [PMID: 25952953 DOI: 10.1002/smll.201500562] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2015] [Indexed: 06/04/2023]
Abstract
Type 2 diabetes mellitus is characterized by the pathological deposition of fibrillized protein, known as amyloids. It is thought that oligomers and/or amyloid fibrils formed from human islet amyloid polypeptide (hIAPP or amylin) cause cell death by membrane damage. The molecular structure of hIAPP amyloid fibrils is dominated by β-sheet structure, as probed with conventional infrared and Raman vibrational spectroscopy. However, with these techniques it is not possible to distinguish between the core and the surface structure of the fibrils. Since the fibril surface crucially affects amyloid toxicity, it is essential to know its structure. Here the surface molecular structure and amino acid residue composition of hIAPP fibrils are specifically probed with nanoscale resolution using tip-enhanced Raman spectroscopy (TERS). The fibril surface mainly contains unordered or α-helical structures, in contrast to the β-sheet-rich core. This experimentally validates recent models of hIAPP amyloids based on NMR measurements. Spatial mapping of the surface structure reveals a highly heterogeneous surface structure. Finally, TERS can probe fibrils formed on a lipid interface, which is more representative of amyloids in vivo.
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Affiliation(s)
| | - Tanja Deckert-Gaudig
- Leibniz Institute of Photonic Technology, Albert-Einstein-Straße 9, 07745, Jena, Germany
| | - Michael Schleeger
- Department of Molecular Spectroscopy, Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany
| | - Krassimir P Velikov
- Soft Condensed Matter, Debye Institute for Nanomaterials Science, Department of Physics and Astronomy, Utrecht University, Princetonplein 5, 3584, CC, Utrecht, The Netherlands
- Unilever Research Labs, NL-3133 AT Vlaardingen, The Netherlands
| | - Volker Deckert
- Leibniz Institute of Photonic Technology, Albert-Einstein-Straße 9, 07745, Jena, Germany
- Institute for Physical Chemistry and Abbe Center of Photonics, University of Jena, Helmholtzweg 4, 07743, Jena, Germany
| | - Mischa Bonn
- Department of Molecular Spectroscopy, Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany
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31
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Lysophospholipid-containing membranes modulate the fibril formation of the repeat domain of a human functional amyloid, pmel17. J Mol Biol 2014; 426:4074-4086. [PMID: 25451784 DOI: 10.1016/j.jmb.2014.10.009] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2014] [Revised: 09/23/2014] [Accepted: 10/08/2014] [Indexed: 11/23/2022]
Abstract
Pmel17 is an important protein for pigmentation in human skin and eyes. Proteolytic fragments from Pmel17 form fibrils upon which melanin is deposited in melanosomes. The repeat domain (RPT) derived from Pmel17 only forms fibrils under acidic melanosomal conditions. Here, we examined the effects of lipids on RPT aggregation to explore whether intramelanosomal vesicles can facilitate fibrillogenesis. Using transmission electron microscopy, circular dichroism, and fluorescence spectroscopy, we monitored fibril formation at the ultrastructural, secondary conformational, and local levels, respectively. Phospholipid vesicles and lysophospholipid (lysolipid) micelles were employed as membrane mimics. The surfactant-like lysolipids are particularly pertinent due to their high content in melanosomal membranes. Interestingly, RPT aggregation kinetics were influenced only by lysolipid-containing phospholipid vesicles. While both vesicles containing either anionic lysophosphatidylglycerol (LPG) or zwitterionic lysophosphatidylcholine (LPC) stimulate aggregation, LPG exerted a greater effect on reducing the apparent nucleation time. A detailed comparison showed distinct behaviors of LPG versus LPC monomers and micelles plausibly originating from their headgroup hydrogen bonding capabilities. Acceleration and retardation of aggregation were observed for LPG monomers and micelles, respectively. Because a specific interaction between LPG and RPT was identified by intrinsic W423 fluorescence and induced α-helical structure, it is inferred that binding of LPG near the C-terminal amyloid core initiates intermolecular association, whereas stabilization of α-helical conformation inhibits β-sheet formation. Contrastingly, LPC promotes RPT aggregation at both submicellar and micellar concentrations via non-specific binding with undetectable secondary structural change. Our findings suggest that protein-lysolipid interactions within melanosomes may regulate amyloid formation in vivo.
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