title: Human defensins facilitate local unfolding of thermodynamically unstable regions of bacterial protein toxins.
abstract: Defensins are short cationic, amphiphilic, cysteine-rich peptides that constitute the front-line immune defense against various pathogens. In addition to exerting direct antibacterial activities, defensins inactivate several classes of unrelated bacterial exotoxins. To date, no coherent mechanism has been proposed to explain defensins' enigmatic efficiency toward various toxins. In this study, we showed that binding of neutrophil ?-defensin HNP1 to affected bacterial toxins caused their local unfolding, potentiated their thermal melting and precipitation, exposed new regions for proteolysis, and increased susceptibility to collisional quenchers without causing similar effects on tested mammalian structural and enzymatic proteins. Enteric ?-defensin HD5 and ?-defensin hBD2 shared similar toxin-unfolding effects with HNP1, albeit to different degrees. We propose that protein susceptibility to inactivation by defensins is contingent to their thermolability and conformational plasticity and that defensin-induced unfolding is a key element in the general mechanism of toxin inactivation by human defensins.
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA.
authors.forename: Elena
authors.initials: E
authors.lastname: Kudryashova
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA.
authors.forename: Royston
authors.initials: R
authors.lastname: Quintyn
authors.affiliation: Department of Microbiology, The Ohio State University, Columbus, OH 43210, USA; Department of Microbial Infection and Immunity, The Ohio State University, Columbus, OH 43210, USA.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Seveau
authors.affiliation: Institute of Human Virology and Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
authors.forename: Wuyuan
authors.initials: W
authors.lastname: Lu
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA.
authors.forename: Vicki H
authors.initials: VH
authors.lastname: Wysocki
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA. Electronic address: kudryashov.1@osu.edu.
authors.forename: Dmitri S
authors.initials: DS
authors.lastname: Kudryashov
mesh_terms: D000942:Antigens, Bacterial / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism; D001427:Bacterial Toxins / Q000378:metabolism*; D002460:Cell Line; D002918:Chymotrypsin / Q000378:metabolism; D004768:Enterotoxins / Q000378:metabolism; D005098:Exotoxins / Q000378:metabolism*; D006801:Humans; D011485:Protein Binding; D011487:Protein Conformation; D058767:Protein Unfolding; D059748:Proteolysis; D012097:Repressor Proteins / Q000378:metabolism; D013820:Thermolysin / Q000378:metabolism; D023084:alpha-Defensins / Q000276:immunology / Q000378:metabolism* / Q000494:pharmacology*; D023083:beta-Defensins / Q000378:metabolism*
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D001427:Bacterial Toxins; C500225:DEFA5 protein, human; C106641:DEFB4A protein, human; D004768:Enterotoxins; D005098:Exotoxins; D012097:Repressor Proteins; C434464:RtxA protein, Vibrio cholerae; C105615:TcdC protein, Clostridium difficile; D023084:alpha-Defensins; C030325:anthrax toxin; D023083:beta-Defensins; C406413:human neutrophil peptide 1; C041348:tcdA protein, Clostridium difficile; D002918:Chymotrypsin; D013820:Thermolysin