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Author Notes:

Edward H. Egelman, gelman@virginia.edu

Vincent P. Conticello, vcontic@emory.edu

E.H.E. and V.P.C. designed research; M.A.B.K., S.W., L.C.B., A.T., X.Z., E.H.E., and V.P.C. performed research; M.A.B.K., L.C.B., E.H.E., and V.P.C. analyzed data; and M.A.B.K., E.H.E., and V.P.C. wrote the paper.

Cryo-EM imaging of the PSMα3 and PSMβ2 filaments was performed at the Cryo-EM facility at the National Cancer Institute’s Frederick Laboratory for Cancer Research under Contract No. HSSN261200800001E. This study was supported by the Robert P. Apkarian Integrated Electron Microscopy Core at Emory University, which is subsidized by the School of Medicine and Emory College of Arts and Sciences. Additional support was provided by the Georgia Clinical & Translational Science Alliance of the NIH under award number UL1TR000454. Negative-stain TEM images were gathered on a Hitachi HT7700 120kV TEM at Emory University, which was supported by the Georgia Clinical & Translational Science Alliance under award No. UL1TR002378. This research was supported by grants from the NSF (DMR-1534317) to V.P.C. and the NIH (GM122510) to E.H.E. The CD spectropolarimeter was acquired through funding from an NSF grant (DBI-1726544). M.A.B.K. acknowledges financial support from NIH T32 GM080186 and the University of Virginia Robert R. Wagner Fellowship. L.C.B. acknowledges financial support from NIH T32 AI007046. This research used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility, operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We thank Dr. Joseph Wall of Brookhaven National Laboratory for acquisition of the STEM imaging data.

The authors declare no competing interest.

Subject:

Keywords:

  • bacterial pathogenesis
  • cross-α amyloid
  • cryo-EM
  • peptide nanotube
  • Amyloid
  • Bacterial Toxins
  • Cryoelectron Microscopy
  • Humans
  • Nanotubes
  • Peptides
  • Staphylococcus aureus

Phenol-soluble modulins PSMα3 and PSMβ2 form nanotubes that are cross-α amyloids

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Journal Title:

Proceedings of the National Academy of Sciences of the United States of America

Volume:

Volume 119, Number 20

Publisher:

, Pages e2121586119-e2121586119

Type of Work:

Article | Final Publisher PDF

Abstract:

Phenol-soluble modulins (PSMs) are peptide-based virulence factors that play significant roles in the pathogenesis of staphylococcal strains in community-associated and hospital-associated infections. In addition to cytotoxicity, PSMs display the propensity to self-assemble into fibrillar species, which may be mediated through the formation of amphipathic conformations. Here, we analyze the self-assembly behavior of two PSMs, PSMα3 and PSMβ2, which are derived from peptides expressed by methicillin-resistant Staphylococcus aureus (MRSA), a significant human pathogen. In both cases, we observed the formation of a mixture of self-assembled species including twisted filaments, helical ribbons, and nanotubes, which can reversibly interconvert in vitro. Cryo-electron microscopy structural analysis of three PSM nanotubes, two derived from PSMα3 and one from PSMβ2, revealed that the assemblies displayed remarkably similar structures based on lateral association of cross-α amyloid protofilaments. The amphipathic helical conformations of PSMα3 and PSMβ2 enforced a bilayer arrangement within the protofilaments that defined the structures of the respective PSMα3 and PSMβ2 nanotubes. We demonstrate that, similar to amyloids based on cross-β protofilaments, cross-α amyloids derived from these PSMs display polymorphism, not only in terms of the global morphology (e.g., twisted filament, helical ribbon, and nanotube) but also with respect to the number of protofilaments within a given peptide assembly. These results suggest that the folding landscape of PSM derivatives may be more complex than originally anticipated and that the assemblies are able to sample a wide range of supramolecular structural space.

Copyright information:

© 2022 the Author(s). Published by PNAS

This is an Open Access work distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (https://creativecommons.org/licenses/by-nc-nd/4.0/).
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