The membrane-proximal tryptophan-rich region in the transmembrane glycoprotein ectodomain of feline immunodeficiency virus is important for cell entry

Abstract

The mechanisms whereby feline immunodeficiency virus (FIV) adsorbs and enters into susceptible cells are poorly understood. Here, we investigated the role exerted in such functions by the tryptophan (Trp)-rich motif present membrane-proximally in the ectodomain of the FIV transmembrane glycoprotein. Starting from p34TF10, which encodes the entire genome of FIV Petaluma, we produced 11 mutated clones having the Trp-rich motif scrambled or variously deleted or substituted. All mutated progenies adsorbed normally to cells, but the ones with severe disruptions of the motif failed to generate proviral DNA. In the latter mutants, proviral DNA formation was restored by providing an independent source of intact FIV envelope glycoproteins or by addition of the fusing agent polyethylene glycol, thus clearly indicating that their defect resided primarily at the level of cell entry. In addition, the replication-competent mutants exhibited a generally enhanced susceptibility to selected entry inhibitory synthetic peptides, suggestive of a reduced efficiency of the entry step.

Interfacial pre-transmembrane domains in viral proteins promoting membrane fusion and fission

“…Both PreTMs are characterized by negligible mean interfacial hydrophobicity. The presence of several conserved Trp-s within fusogenic FIV gp36 subunit's membrane-proximal sequence was previously noted [41,42]. These hydrophobic-at-interface residues are inter-dispersed with helical periodicity by charged residues that bear the lowest tendency to partitioning into membrane interfaces (Table 1).…”

Antibodies Generated in Cats by a Lipopeptide Reproducing the Membrane-Proximal External Region of the Feline Immunodeficiency Virus Transmembrane Enhance Virus Infectivity

“…Upon virus interaction with susceptible cells, the MPER of FIV is believed to undergo a series of conformational changes similar to the ones, described in much more detail (9,14,16,35), that are known to occur during cell entry in the corresponding region of HIV-1. Thus, theoretically, antibodies reactive against this region may interact not only with epitopes present in resting virions but also with epitopes expressed more or less transiently in the course of cell entry.…”

“…This, coupled with the circumstance that some of the few monoclonal antibodies with broad HIV-1-neutralizing activity recognize epitopes in this region (5,36,40,58), has led others to propose MPER as an interesting target on which to model candidate protective immunogens and antivirals (57). In recent studies, we and others have demonstrated that the MPER of feline immunodeficiency virus (FIV), a naturally occurring lentivirus (41) intensively studied as a model system with which criteria for antiviral vaccines and drugs development can be tested (10,55), shares important structural and functional features with the corresponding domain of HIV-1 (7,14,16,35,38,47,49,50,52). In addition, short synthetic peptides reproducing the MPER of FIV have been shown to inhibit the infectivity of this virus both in vitro and in vivo as a result of blocking cell entry (15,17).…”

Targeting HIV-1 gp41 in Close Proximity to the Membrane Using Antibody and Other Molecules

“…Hydrophobic, Trp-rich MPER sequences are a particularly conserved feature among lentiviruses [64], so a fusion inhibitor strategy for the MPER could potentially be generalizable. Similar to HIV-1, the MPER of feline immunodeficiency virus (FIV) gp36 contains three conserved Trp residues, interacts with lipid bilayers, and deletion, scrambling, or mutation of the Trp residues results in a non-functional protein [171][172][173]. Interestingly, peptides corresponding to the FIV MPER can inhibit FIV infection in vitro, and peptides truncated to an 8-mer (C8) that centers around three Trp residues still retain full antiviral activity (IC 50 of 0.03-0.63 g/ml against 12 primary FIV isolates) [174,175].…”