Mechanism of Adenovirus Neutralization by Human α-Defensins

Abstract

Defensins are naturally occurring antimicrobial peptides that disrupt bacterial membranes and prevent bacterial invasion of the host. Emerging studies indicate that certain defensins also block virus infection; however, the mechanism(s) involved are poorly understood. We demonstrate that human alpha-defensins inhibit adenovirus infection at low micromolar concentrations, and this requires direct association of the defensin with the virus. Moreover, defensins inhibit virus disassembly at the vertex region, thereby restricting the release of an internal capsid protein, pVI, which is required for endosomal membrane penetration during cell entry. As a consequence, defensins hamper the release of adenovirus particles from endocytic vesicles, resulting in virion accumulation in early endosomes and lysosomes. Thus, defensins possess remarkably distinct modes of activity against bacteria and viruses, and their function may provide insights for the development of new antiviral strategies.

Adenovirus Composition, Proteolysis, and Disassembly Studied by In-depth Qualitative and Quantitative Proteomics

“…The virus was dialyzed into DX10/10 buffer (40 mM Tris, pH 8.1, 500 mM NaCl, 10% glycerol, 10% ethylene glycol, 2% sucrose, and 1% mannitol). Partial capsid disassembly was achieved using thermal perturbation (34,35). Briefly, Ad5F35 (5 mg) was diluted in 7.5 mM HEPES, 50 mM NaCl, pH 7.4, divided into 6 ϫ 500 l aliquots, and incubated at 55°C for 15 min.…”

“…Data collection was done with Channel 1/FAM settings (450 -490 nm excitation and 510 -530 nm emission). Measurements of capsid disassembly via immunoblot with antibodies to protein VI or fiber was done as described previously (34,35).…”

Multivalent Binding of Carbohydrates by the Human α-Defensin, HD5

“…HD5 did not block virion binding or internalization, instead acting by preventing the escape of virions from their endocytic vesicles (36). HD5 inhibits adenovirus infections by binding to the virus capsid and preventing its subsequent uncoating, an event the virus requires to escape the endosomal compartment and enter the cytosol (37). HD5 and HNP1 also inhibit infection by BK polyoma virus, a cause of interstitial nephritis in immunosuppressed renal transplant recipients, evidently acting by binding to the virions and agglutinating them (38).…”

Trp-26 Imparts Functional Versatility to Human α-Defensin HNP1

“…Yet cationicity alone does not explain the strain selectivity of different defensins. Furthermore, unlike human ␣-defensins and (perhaps) HBD3, the more positively charged ␤-defensins are not lectins and do not inhibit bacterial toxins and many viruses (31)(32)(33)(34)(35)(36).…”