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Brain and Behavior (1)
Cell Stress & Chaperones (1)
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Kawata, Yasushi (3)
Mizobata, Tomohiro (3)
Hongo, Kunihiro (2)
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Yagi, Hisashi (1)
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Role of C-terminal negative charges and tyrosine residues in fibril formation of α-synuclein
Brain and Behavior
α-Synuclein (140 amino acids), one of the causative proteins of Parkinson's disease, forms amyloid fibrils in brain neuronal cells. In order to further explore the contributions of the C-terminal region of α-synuclein in fibril formation and also to understand the overall mechanism of fibril formation, we reduced the number of negatively charged residues in the C-terminal region using mutagenesis. Mutants with negative charges deleted displayed accelerated fibril formation compared with wild-type α-synuclein, demonstrating that negative charges located in the C-terminal region of α-synuclein modulate fibril formation. Additionally, when tyrosine residues located at position 125, 133, and 136 in the C-terminal region were changed to alanine residue(s), we found that all mutants containing the Tyr136Ala mutation showed delays in fibril formation compared with wild type. Mutation of Tyr136 to various amino acids revealed that aromatic residues located at this position act favorably toward fibril formation. In mutants where charge neutralization and tyrosine substitution were combined, we found that these two factors influence fibril formation in complex fashion. These findings highlight the importance of negative charges and aromatic side chains in the C-terminal region of α-synuclein in fibril formation.
Amyloid; amyloid formation mechanism; Parkinson's disease; protein aggregation; site-directed mutagenesis; α-Synuclein
Probing the Functional Mechanism of Escherichia coli GroEL Using Circular Permutation
Uversky, Vladimir N.
The Escherichia coli chaperonin GroEL subunit consists of three domains linked via two hinge regions, and each domain is responsible for a specific role in the functional mechanism. Here, we have used circular permutation to study the structural and functional characteristics of the GroEL subunit.
Three soluble, partially active mutants with polypeptide ends relocated into various positions of the apical domain of GroEL were isolated and studied. The basic functional hallmarks of GroEL (ATPase and chaperoning activities) were retained in all three mutants. Certain functional characteristics, such as basal ATPase activity and ATPase inhibition by the cochaperonin GroES, differed in the mutants while at the same time, the ability to facilitate the refolding of rhodanese was roughly equal. Stopped-flow fluorescence experiments using a fluorescent variant of the circularly permuted GroEL CP376 revealed that a specific kinetic transition that reflects movements of the apical domain was missing in this mutant. This mutant also displayed several characteristics that suggested that the apical domains were behaving in an uncoordinated fashion.
The loss of apical domain coordination and a concomitant decrease in functional ability highlights the importance of certain conformational signals that are relayed through domain interlinks in GroEL. We propose that circular permutation is a very versatile tool to probe chaperonin structure and function.
Purification and characterization of chaperonins 60 and 10 from Methylobacillus glycogenes
Cell Stress & Chaperones
Two proteins belonging to the group I chaperonin family were isolated from an obligate methanotroph, Methylobacillus glycogenes. The two proteins, one a GroEL homologue (cpn60: M. glycogenes 60 kDa chaperonin) and the other a GroES homologue (cpn10: M. glycogenes 10 kDa chaperonin), composed a heteropolymeric complex in the presence of ATP. Both proteins were purified from crude extracts of M. glycogenes by anion-exchange (DEAE-Toyopearl) and gel-filtration (Sephacryl S-400) chromatography. The native molecular weights of each chaperonin protein as determined by high-performance liquid chromatography (HPLC) gel-filtration were 820 000 for cpn60 and 65 000 for cpnl0. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the subunit molecular weights of cpn60 and cpnl0 were 58 000 and 10 000, respectively. Both cpn60 and cpnl0 possessed amino acid sequences which were highly homologous to other group I chaperonins. M. glycogenes cpn60 displayed an ATPase activity which was inhibited in the presence of cpn10. The chaperonins also displayed an ability to interact with and facilitate the refolding of Thermus malate dehydrogenase and yeast enolase in a manner similar to that of GroEL/ES. The similarities between the Escherichia coli GroE proteins are discussed.
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