Fibril formation of hsp10 homologue proteins and determination of fibril core regions: differences in fibril core regions dependent on subtle differences in amino acid sequence

Structural basis of Cu, Zn-superoxide dismutase amyloid fibril formation involves interaction of multiple peptide core regions

Cu, Zn-superoxide dismutase (SOD1), an enzyme implicated in the progression of familial amyotrophic lateral sclerosis (fALS), forms amyloid fibrils under certain experimental conditions. As part of our efforts to understand ALS pathogenesis, in this study we found that reduction of the intramolecular disulfide bond destabilized the tertiary structure of metal free wild-type SOD1 and greatly enhanced fibril formation in vitro. We also identified fibril core peptides that are resistant to protease digestion by using mass spectroscopy and Edman degradation analyses. Three regions dispersed throughout the sequence were detected as fibril core sequences of SOD1. Interestingly, by using three synthetic peptides that correspond to these identified regions, we determined that each region was capable of fibril formation, either alone or in a mixture containing multiple peptides. It was also revealed that by reducing the disulfide bond and causing a decrease in the structural stability, the amyloid fibril formation of a familial mutant SOD1 G93A was accelerated even under physiological conditions. These results demonstrate that by destabilizing the structure of SOD1 by removing metal ions and breaking the intramolecular disulfide bridge, multiple fibril-forming core regions are exposed, which then interact with each another and form amyloid fibrils under physiological conditions.

Dual functions in response to heat stress and spermatogenesis: characterization of expression profile of small heat shock proteins 9 and 10 in goat testis

Small heat shock proteins 9 and 10 (HSPB9 and HSPB10) are two testis-specific expressed sHsps. The objective of this study was to investigate the mRNA expression profile of HSPB9 and HSPB10 in goat testis among the different seasons, ages, and environmental temperatures. Allocation of the two sHsps was also performed by immunohistochemistry. The results showed that the transcript levels of HSPB9 and HSPB10 were extremely high in the testis (P < 0.01). The relative expression of HSBP9 and HSPB10 in testis showed a tendency to increase with age and then is maintained at the constant level after sexual maturity. HSPB9 and HSPB10 have significantly higher expression in the breeding season  (P < 0.05) and hot season (P < 0.01). Both HSPB9 and HSPB10 were found to be upregulated by high-temperature stress in testis (P < 0.05), and the expressions of Hsp70 and Hsp90 were also increased simultaneously (P < 0.01). Immunohistochemistry analysis localized HSPB9 expressed in spermatogonia, spermatocytes, and round spermatids and HSPB10 expressed in the elongate spermatids. In epididymis, strongly staining signal of HSPB10 was detected in pseudostratified columnar epithelium. In conclusion, the two testis-specific sHsps are closely related to male reproduction and heat tolerance. The results could provide valuable data for the further studies on HSPB9 and HSPB10.

Gene expression of Hsps in normal and abnormal embryonic development of mouse hindlimbs

Heat shock proteins (Hsps), which have important biological functions, are a class of highly conserved genetic molecules with the capacity of protecting and promoting cells to repair themselves from damage caused by various stimuli. Our previous studies found that Hsp25, HspB2, HspB3, HspB7, Hsp20, HspB9, HspB10, and Hsp40 may be related to all-trans retinoic acid (atRA)-induced phocomelic and other abnormalities, while HspA12B, HspA14, Trap1, and Hsp105 may be forelimb development-related genes; Grp78 may play an important role in forelimb development. In this study, the embryonic phocomelic, oligodactylic model of both forelimbs and hindlimbs was developed by atRA administered per os to the pregnant mice on gestational day 11, and the expression of 36 members of Hsps family in normal and abnormal development of embryonic hindlimbs was measured by real-time fluorescent quantitative polymerase chain reaction (qRT-PCR). It is found that HspA1L, Hsp22, Hsp10, Hsp60, Hsp47, HspB2, HspB10, HspA12A, Apg1, HspB4, Grp78, and HspB9 probably performs a major function in limb development, and HspA13, Grp94 and Hsp110 may be hindlimb development-related genes.

Amyloid fibril formation in vitro from halophilic metal binding protein: its high solubility and reversibility minimized formation of amorphous protein aggregations

Halophilic proteins are characterized by high net negative charges and relatively small fraction of hydrophobic amino acids, rendering them aggregation resistant. These properties are also shared by histidine-rich metal binding protein (HP) from moderate halophile, Chromohalobacter salexigens, used in this study. Here, we examined how halophilic proteins form amyloid fibrils in vitro. His-tagged HP, incubated at pH 2.0 and 58°C, readily formed amyloid fibrils, as observed by thioflavin fluorescence, CD spectra, and transmission or atomic force microscopies. Under these low-pH harsh conditions, however, His-HP was promptly hydrolyzed to smaller peptides most likely responsible for rapid formation of amyloid fibril. Three major acid-hydrolyzed peptides were isolated from fibrils and turned out to readily form fibrils. The synthetic peptides predicted to form fibrils in these peptide sequences by Waltz software also formed fibrils. Amyloid fibril was also readily formed from full-length His-HP when incubated with 10-20% 2,2,2-trifluoroethanol at pH 7.8 and 25°C without peptide bond cleavage.

Role of C-terminal negative charges and tyrosine residues in fibril formation of α-synuclein

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.

Covalent structural changes in unfolded GroES that lead to amyloid fibril formation detected by NMR: insight into intrinsically disordered proteins

Co-chaperonin GroES from Escherichia coli works with chaperonin GroEL to mediate the folding reactions of various proteins. However, under specific conditions, i.e. the completely disordered state in guanidine hydrochloride, this molecular chaperone forms amyloid fibrils similar to those observed in various neurodegenerative diseases. Thus, this is a good model system to understand the amyloid fibril formation mechanism of intrinsically disordered proteins. Here, we identified a critical intermediate of GroES in the early stages of this fibril formation using NMR and mass spectroscopy measurements. A covalent rearrangement of the polypeptide bond at Asn(45)-Gly(46) and/or Asn(51)-Gly(52) that eventually yield β-aspartic acids via deamidation of asparagine was observed to precede fibril formation. Mutation of these asparagines to alanines resulted in delayed nucleus formation. Our results indicate that peptide bond rearrangement at Asn-Gly enhances the formation of GroES amyloid fibrils. The finding provides a novel insight into the structural process of amyloid fibril formation from a disordered state, which may be applicable to intrinsically disordered proteins in general.

Isolation of short peptide fragments from alpha-synuclein fibril core identifies a residue important for fibril nucleation: a possible implication for diagnostic applications

alpha-Synuclein is one of the causative proteins of the neurodegenerative disorder, Parkinson's disease. Deposits of alpha-synuclein called Lewy bodies are a hallmark of this disorder, which is implicated in its progression. In order to understand the mechanism of amyloid fibril formation of alpha-synuclein in more detail, in this study we have isolated a specific, ~20 residue peptide region of the alpha-synuclein fibril core, using a combination of Edman degradation and mass-spectroscopy analyses of protease-resistant samples. Starting from this core peptide sequence, we then synthesized a series of peptides that undergo aggregation and fibril formation under similar conditions. Interestingly, in a derivative peptide where a crucial phenylalanine residue was changed to a glycine, the ability to initiate spontaneous fibril formation was abolished, while the ability to extend from preexisting fibril seeds was conserved. This fibril extension occurred irrespective of the source of the initial fibril seed, as demonstrated in experiments using fibril seeds of insulin, lysozyme, and GroES. This interesting ability suggests that this peptide might form the basis for a possible diagnostic tool useful in detecting the presence of various fibrillogenic factors.