Biophysical Society Conference | Tahoe 2023

Proton Reactions: From Basic Science to Biomedical Applications

Tuesday Speaker Abstracts

PEPTIDE NANOPORES ARE STABILIZED BY A COOPERATUVE NETWORK OF HYDROGEN BONDS

Ana Nicoleta Bondar 3 ; Kalina Hristova 2 ; William C Wimley 1 ; 1 Tulane University, Biochemistry, New Orleans, LA, USA 2 Johns Hopkins University, Materials Science, Baltimore, MD, USA 3 University of Bucharest, Physics, Bucharest, Romania

We have been using synthetic molecular evolution (generations of iterative library design and screening) to evolve peptides that self-assemble into large macromolecule-sized (5-10 nm diameter) “nanopores” that are controllable and membrane-selective. Specifically, we have identified the pHD peptides that self-assemble into nanopores in lipid bilayers at very low concentration, triggered by mildly acidic pH. We also evolved the closely related macrolittins, which have the same activity, but are not pH sensitive. Such peptide nanopore formation is unprecedented. These peptides fold into α -helices that, despite multiple charged and polar residues, insert into membrane-spanning configurations and stabilize the perimeter of large water-filled pores. Classical textbook concepts of protein folding in membranes do not predict this structure because the peptides appear to be too polar, overall, to stably insert across membranes. Since hydrophobicity alone does not account for their stability in membranes, these nanopores must also be stabilized by other interactions. Individual sidechain H-bonds in contact with bulk water, are relatively weak. But our atomistic molecular dynamics (MD) simulations show that charged and polar groups that are densely located along the fully hydrated inner surfaces of the nanopore form dynamical, yet persistent, cooperative H-bond networks between peptides, lipid headgroups, and water. The headgroups of multiple lipid molecules with unusual orientations participate in the H-bond network and stabilize the nanopore. No previously described H-bond network in membranes is as extensive as the one we have identified in the pHD peptide and macrolittin nanopore structures. These nanopore forming peptides may represent a new type of membrane protein structure.

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