Ribonuclease A suggests how proteins self-chaperone against amyloid fiber formation

Authors

  • Poh K. Teng,

    1. Departments of Chemistry & Biochemistry and Biological Chemistry, Howard Hughes Medical Institute, UCLA-DOE Institute for Genomics and Proteomics, Los Angeles, CA 90095-1570
    Current affiliation:
    1. Molecular and Cell Biology Department, University of California Berkeley, Berkeley, CA 94720
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  • Natalie J. Anderson,

    1. Departments of Chemistry & Biochemistry and Biological Chemistry, Howard Hughes Medical Institute, UCLA-DOE Institute for Genomics and Proteomics, Los Angeles, CA 90095-1570
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  • Lukasz Goldschmidt,

    1. Departments of Chemistry & Biochemistry and Biological Chemistry, Howard Hughes Medical Institute, UCLA-DOE Institute for Genomics and Proteomics, Los Angeles, CA 90095-1570
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  • Michael R. Sawaya,

    1. Departments of Chemistry & Biochemistry and Biological Chemistry, Howard Hughes Medical Institute, UCLA-DOE Institute for Genomics and Proteomics, Los Angeles, CA 90095-1570
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  • Shilpa Sambashivan,

    1. Departments of Chemistry & Biochemistry and Biological Chemistry, Howard Hughes Medical Institute, UCLA-DOE Institute for Genomics and Proteomics, Los Angeles, CA 90095-1570
    Current affiliation:
    1. Department of Neuroscience, Amgen Inc, 1120 Veterans Boulevard, South San Francisco, CA 94080
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  • David Eisenberg

    Corresponding author
    1. Departments of Chemistry & Biochemistry and Biological Chemistry, Howard Hughes Medical Institute, UCLA-DOE Institute for Genomics and Proteomics, Los Angeles, CA 90095-1570
    • 201A Boyer Hall, Department of Chemistry and Biochemistry, University of California, 611 Charles Young Drive East, Los Angeles, CA 90095-1569

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Abstract

Genomic analyses have identified segments with high fiber-forming propensity in many proteins not known to form amyloid. Proteins are often protected from entering the amyloid state by molecular chaperones that permit them to fold in isolation from identical molecules; but, how do proteins self-chaperone their folding in the absence of chaperones? Here, we explore this question with the stable protein ribonuclease A (RNase A). We previously identified fiber-forming segments of amyloid-related proteins and demonstrated that insertion of these segments into the C-terminal hinge loop of nonfiber-forming RNase A can convert RNase A into the amyloid state through three-dimensional domain-swapping, where the inserted fiber-forming segments interact to create a steric zipper spine. In this study, we convert RNase A into amyloid-like fibers by increasing the loop length and hence conformational freedom of an endogenous fiber-forming segment, SSTSAASS, in the N-terminal hinge loop. This is accomplished by sandwiching SSTSAASS between inserted Gly residues. With these inserts, SSTSAASS is now able to form the steric zipper spine, allowing RNase A to form amyloid-like fibers. We show that these fibers contain RNase A molecules retaining their enzymatic activity and therefore native-like structure. Thus, RNase A appears to prevent fiber formation by limiting the conformational freedom of this fiber-forming segment from entering a steric zipper. Our observations suggest that proteins have evolved to self-chaperone by using similar protective mechanisms.

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