title: Theta-defensins prevent HIV-1 Env-mediated fusion by binding gp41 and blocking 6-helix bundle formation.
abstract: Retrocyclin-1, a -defensin, protects target cells from human immunodeficiency virus, type 1 (HIV-1) by preventing viral entry. To delineate its mechanism, we conducted fusion assays between susceptible target cells and effector cells that expressed HIV-1 Env. Retrocyclin-1 (4 microm) completely blocked fusion mediated by HIV-1 Envs that used CXCR4 or CCR5 but had little effect on cell fusion mediated by HIV-2 and simian immunodeficiency virus Envs. Retrocyclin-1 inhibited HIV-1 Env-mediated fusion without impairing the lateral mobility of CD4, and it inhibited the fusion of CD4-deficient cells with cells bearing CD4-independent HIV-1 Env. Thus, it could act without cross-linking membrane proteins or inhibiting gp120-CD4 interactions. Retrocyclin-1 acted late in the HIV-1 Env fusion cascade but prior to 6-helix bundle formation. Surface plasmon resonance experiments revealed that retrocyclin bound the ectodomain of gp41 with high affinity in a glycan-independent manner and that it bound selectively to the gp41 C-terminal heptad repeat. Native-PAGE, enzyme-linked immunosorbent assay, and CD spectroscopic analyses all revealed that retrocyclin-1 prevented 6-helix bundle formation. This mode of action, although novel for an innate effector molecule, resembles the mechanism of peptidic entry inhibitors based on portions of the gp41 sequence.
authors.affiliation: Center for Cancer Research Nanobiology Program, NCI-Frederick, National Institutes of Health, Frederick, Maryland 21702, USA.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Gallo
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Satinder S
authors.initials: SS
authors.lastname: Rawat
authors.forename: Grace
authors.initials: G
authors.lastname: Jung
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Waring
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Cole
authors.forename: Hong
authors.initials: H
authors.lastname: Lu
authors.forename: Xuxia
authors.initials: X
authors.lastname: Yan
authors.forename: Norelle L
authors.initials: NL
authors.lastname: Daly
authors.forename: David J
authors.initials: DJ
authors.lastname: Craik
authors.forename: Shibo
authors.initials: S
authors.lastname: Jiang
authors.forename: Robert I
authors.initials: RI
authors.lastname: Lehrer
authors.forename: Robert
authors.initials: R
authors.lastname: Blumenthal
mesh_terms: D001665:Binding Sites; D023082:Defensins / Q000378:metabolism / Q000494:pharmacology*; D015700:HIV Envelope Protein gp41 / Q000378:metabolism; D023581:HIV Fusion Inhibitors / Q000378:metabolism / Q000494:pharmacology*; D015658:HIV Infections / Q000188:drug therapy / Q000821:virology; D015497:HIV-1 / Q000187:drug effects* / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D011485:Protein Binding; D011487:Protein Conformation; D014779:Virus Replication / Q000187:drug effects* / Q000235:genetics
chemical_list: D023082:Defensins; D015700:HIV Envelope Protein gp41; D023581:HIV Fusion Inhibitors; C450142:theta-defensin