Masatoshi Saiki

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The mammalian endoplasmic reticulum (ER) harbors disulfide bond-generating enzymes, including Ero1α and peroxiredoxin 4 (Prx4), and nearly 20 members of the protein disulfide isomerase family (PDIs), which together constitute a suitable environment for oxidative protein folding. Here, we clarified the Prx4 preferential recognition of two PDI family(More)
Protein folding occurs simultaneously with disulfide bond formation. In general, the in vitro folding of proteins containing disulfide bond(s) is carried out in the presence of redox reagents, such as glutathione, to permit native disulfide pairing to occur. It is well known that the formation of a disulfide bond and the correct tertiary structure of a(More)
Prion diseases represent fatal neurodegenerative disorders caused by the aggregation of prion proteins. With regard to the formation of the amyloidogenic cross-β-structure, the initial mechanism in the conversion to a β-structure is critically important. To explore the core regions forming a stem of the amyloid, we designed and prepared a series of peptides(More)
Various mutants of the protein fragment, barnase module-1 (1-24) were investigated in order to reveal the structural principle of amyloid-like fibrils. By means of circular dichroism spectroscopy, X-ray diffraction, electron microscopy, and thioflavin T binding assay, we found that the molecules containing two beta-strands and an intervening turn structure(More)
In order to reveal the requirements for amino acid sequences prone to form amyloid fibrils, a novel prediction method based on the original structural model of amyloids was developed. As a working hypothesis, two fundamental conditions were introduced into the design of the present system for the evaluation of the propensity for amyloidogenicity. The first(More)
The mammalian endoplasmic reticulum (ER) contains a diverse oxidative protein folding network in which ERp46, a member of the protein disulfide isomerase (PDI) family, serves as an efficient disulfide bond introducer together with Peroxiredoxin-4 (Prx4). We revealed a radically different molecular architecture of ERp46, in which the N-terminal two(More)
Peptidylarginine deiminase IV (PAD4) catalyzes the conversion of an Arg residue to a citrulline residue in various proteins. In particular, citrullination of histone subunits, such as H2A and H3, by PAD4 is thought to be related to rheumatoid arthritis. However, the details of the citrullination mechanism of histone H2A and H3 are not yet well known.(More)
Amyloid fibrils are fibrous protein assemblies with distinctive cross-β structures. For amyloidosis, there are disease-associated mutations outside of the cross-β structures. Thus, it is necessary to elucidate the role of peripheral sequences outside the cross-β structure. Amyloid fibrils are generally 10nm in width; however, the amyloid fibrils of(More)
Dragline silk is a high-performance biopolymer with exceptional mechanical properties. Artificial spider dragline silk is currently prepared by a recombinant technique or chemical synthesis. However, the recombinant process is costly and large-sized synthetic peptides are needed for fiber formation. In addition, the silk fibers that are produced are much(More)
The role of the peripheral sequence neighboring the core cross-beta region was investigated using a peptide library constructed with all possible combinations of Lys, Glu, Ser, and Leu at three residue positions (X1-X3) forming the N-terminal region linked to the amyloid core sequence of the barnase-derived segment (A4-K22). By means of CD spectra and(More)
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