The Amphibian Antimicrobial Peptide Uperin 3.5 is a Cross-α/Cross-β Chameleon Functional Amyloid

Abstract

Antimicrobial activity is being increasingly linked to amyloid fibril formation, suggesting physiological roles for some human amyloids, which have historically been viewed as strictly pathological agents. This work reports on formation of functional cross-α amyloid fibrils of the amphibian antimicrobial peptide uperin 3.5 at atomic-resolution, an architecture initially discovered in the bacterial PSMα3 cytotoxin. The fibrils of uperin 3.5 and PSMα3 were comprised of parallel and anti-parallel helical sheets, respectively, recapitulating properties of β-sheets.Uperin 3.5 helical fibril formation was largely induced by, and formed on, bacterial cells or membrane mimetics, and led to membrane damage and cell death. Uperin 3.5 demonstrated chameleon properties, with a secondary structure switch to cross-β fibrils with reduced antibacterial activity in the absence of lipids or after heat shock. These findings suggest a regulation mechanism, which includes storage of inactive peptides as well as environmentally induced activation of uperin 3.5, via chameleon cross-α/β amyloid fibrils.

Fragment-based ab initio phasing of peptidic nanocrystals by MicroED

“…Knowledge-based and modeled libraries rendered higher Z-scores than general libraries, discriminating as illustrated in Fig2B, F. This makes the present strategy amenable to exploring distinct secondary structure motifs, including primarily ɑ-helical peptides or structures with more than one type of secondary structure 29,30 .…”

Rare by Natural Selection: Tunable Disulfide-bonded Supramolecular Antimicrobials Peptides

“…Moreover, the bacterial membranes and cell walls might differentially affect aggregation and fibril morphology, thereby altering toxicity level. Bi-directional effects between membrane lipids and fibril-forming toxins have been previously suggested for the bacterial PSMa3 cytotoxin and the amphibian uperin 3.5 AMP which form helical cross-α amyloid fibrils 42,52,53 .…”

“…We designed eight single-point cysteine mutations in different structural locations in hLL-3717-29 and analyzed their antibiotic activity against four bacterial strains, along with their sensitivity to reducing conditions. The observations were supported by cysteine substitutions in the amphibian uperin 3.5, another AMP that forms supramolecular structures, specifically of amyloid fibrils with a functional secondary structure switch between cross-a and cross-b configurations 42 . We further determined the atomic structure of a cysteine mutant at the center of the helical hydrophobic moment, the most deeply buried position in the assembly of hLL-3717-29 41 .…”

Natural Antimicrobial Peptides Self-assemble as α/β Chameleon Amyloids

“…Several AMPs assemble into well-ordered fibrils with amyloidogenic features such as amyloidindicator dye binding and cross- structures of tightly mated -sheets [3][4][5][6][7][8][9][10] . Correspondingly, human amyloids associated with neurodegenerative and systemic diseases demonstrate antimicrobial activity, including amyloid- (A) and tau involved in Alzheimer's disease, -synuclein involved in Parkinson's disease, serum amyloid A and beta2-microglobulin associated with systemic amyloidosis, human islet amyloid polypeptide involved in diabetes, and the human prion protein [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] .…”

“…The amyloid-forming uperin 3.5 8,[28][29][30] showed a secondary structure switch between cross- and cross- fibrils, depending on environmental conditions. In particular, exposure to lipids and surfactants drove a transition to an α-helical state 8,31 . We recently determined the high-resolution structure of the cross- form of uperin 3.5 by cryogenic electron microscopy (cryo-EM) 32 .…”