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Sakunthala A, Datta D, Navalkar A, Gadhe L, Kadu P, Patel K, Mehra S, Kumar R, Chatterjee D, Devi J, Sengupta K, Padinhateeri R, Maji SK. Direct Demonstration of Seed Size-Dependent α-Synuclein Amyloid Amplification. J Phys Chem Lett 2022; 13:6427-6438. [PMID: 35816132 DOI: 10.1021/acs.jpclett.2c01650] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The size of amyloid seeds is known to modulate their autocatalytic amplification and cellular toxicity. However, the seed size-dependent secondary nucleation mechanism, toxicity, and disease-associated biological processes mediated by α-synuclein (α-Syn) fibrils are largely unknown. Using the cellular model and in vitro reconstitution, we showed that the size of α-Syn fibril seeds dictates not only their cellular internalization and associated cell death but also the distinct mechanisms of fibril amplification pathways involved in the pathological conformational change of α-Syn. Specifically, small fibril seeds showed elongation possibly through monomer addition at the fibril termini, whereas longer fibrils template the fibril amplification by surface-mediated nucleation as demonstrated by super-resolution microscopy. The distinct mechanism of fibril amplification and cellular uptake along with toxicity suggest that breakage of fibrils into seeds of different sizes determines the underlying pathological outcome of synucleinopathies.
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Affiliation(s)
- Arunima Sakunthala
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Debalina Datta
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Ambuja Navalkar
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Laxmikant Gadhe
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Pradeep Kadu
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Komal Patel
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Surabhi Mehra
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Rakesh Kumar
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Debdeep Chatterjee
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Jyoti Devi
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Kundan Sengupta
- Chromosome Biology Lab, Indian Institute of Science Education and Research, Pune 411008, India
| | - Ranjith Padinhateeri
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Samir K Maji
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
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Melanosomal formation of PMEL core amyloid is driven by aromatic residues. Sci Rep 2017; 7:44064. [PMID: 28272432 PMCID: PMC5341037 DOI: 10.1038/srep44064] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Accepted: 02/01/2017] [Indexed: 12/05/2022] Open
Abstract
PMEL is a pigment cell protein that forms physiological amyloid in melanosomes. Many amyloids and/or their oligomeric precursors are toxic, causing or contributing to severe, incurable diseases including Alzheimer’s and prion diseases. Striking similarities in intracellular formation pathways between PMEL and various pathological amyloids including Aβ and PrPSc suggest PMEL is an excellent model system to study endocytic amyloid. Learning how PMEL fibrils assemble without apparent toxicity may help developing novel therapies for amyloid diseases. Here we identify the critical PMEL domain that forms the melanosomal amyloid core (CAF). An unbiased alanine-scanning screen covering the entire region combined with quantitative electron microscopy analysis of the full set of mutants uncovers numerous essential residues. Many of these rely on aromaticity for function suggesting a role for π-stacking in melanosomal amyloid assembly. Various mutants are defective in amyloid nucleation. This extensive data set informs the first structural model of the CAF and provides insights into how the melanosomal amyloid core forms.
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Walker AS, Rablen PX, Schepartz A. Rotamer-Restricted Fluorogenicity of the Bis-Arsenical ReAsH. J Am Chem Soc 2016; 138:7143-50. [PMID: 27163487 PMCID: PMC5381806 DOI: 10.1021/jacs.6b03422] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Fluorogenic dyes such as FlAsH and ReAsH are used widely to localize, monitor, and characterize proteins and their assemblies in live cells. These bis-arsenical dyes can become fluorescent when bound to a protein containing four proximal Cys thiols-a tetracysteine (Cys4) motif. Yet the mechanism by which bis-arsenicals become fluorescent upon binding a Cys4 motif is unknown, and this nescience limits more widespread application of this tool. Here we probe the origins of ReAsH fluorogenicity using both computation and experiment. Our results support a model in which ReAsH fluorescence depends on the relative orientation of the aryl chromophore and the appended arsenic chelate: the fluorescence is rotamer-restricted. Our results do not support a model in which fluorogenicity arises from the relief of ring strain. The calculations identify those As-aryl rotamers that support fluorescence and those that do not and correlate well with prior experiments. The rotamer-restricted model we propose is supported further by biophysical studies: the excited-state fluorescence lifetime of a complex between ReAsH and a protein bearing a high-affinity Cys4 motif is longer than that of ReAsH-EDT2, and the fluorescence intensity of ReAsH-EDT2 increases in solvents of increasing viscosity. By providing a higher resolution view of the structural basis for fluorogenicity, these results provide a clear strategy for the design of more selective bis-arsenicals and better-optimized protein targets, with a concomitant improvement in the ability to characterize previously invisible protein conformational changes and assemblies in live cells.
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Affiliation(s)
- Allison S. Walker
- Department of Chemistry, Yale University, 225 Prospect St., New Haven CT 06520
| | - Paul X. Rablen
- Department of Chemistry & Biochemistry, Swarthmore College, 500 College Ave., Swarthmore, PA 19081
| | - Alanna Schepartz
- Department of Chemistry, Yale University, 225 Prospect St., New Haven CT 06520
- Department of Molecular, Cellular, and Developmental Biology, Yale University, 225 Prospect St., New Haven CT 06520
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Salipalli S, Singh PK, Borlak J. Recent advances in live cell imaging of hepatoma cells. BMC Cell Biol 2014; 15:26. [PMID: 25005127 PMCID: PMC4108253 DOI: 10.1186/1471-2121-15-26] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2013] [Accepted: 06/25/2014] [Indexed: 11/10/2022] Open
Abstract
Live cell imaging enables the study of dynamic processes of living cells in real time by use of suitable reporter proteins and the staining of specific cellular structures and/or organelles. With the availability of advanced optical devices and improved cell culture protocols it has become a rapidly growing research methodology. The success of this technique relies mainly on the selection of suitable reporter proteins, construction of recombinant plasmids possessing cell type specific promoters as well as reliable methods of gene transfer. This review aims to provide an overview of the recent developments in the field of marker proteins (bioluminescence and fluorescent) and methodologies (fluorescent resonance energy transfer, fluorescent recovery after photobleaching and proximity ligation assay) employed as to achieve an improved imaging of biological processes in hepatoma cells. Moreover, different expression systems of marker proteins and the modes of gene transfer are discussed with emphasis on the study of lipid droplet formation in hepatocytes as an example.
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Affiliation(s)
| | | | - Jürgen Borlak
- Centre for Pharmacology and Toxicology, Hannover Medical School, Carl-Neuberg-Str, 1, 30625 Hannover, Germany.
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