Identification of a Receptor-Binding Pocket on the Envelope Protein of Friend Murine Leukemia Virus

Abstract

Based on previous structural and functional studies, a potential receptor-binding site composed of residues that form a pocket at one end of the two long antiparallel helices in the receptor-binding domain of Friend 57 murine leukemia virus envelope protein (RBD) has been proposed. To test this hypothesis, directed substitutions for residues in the pocket were introduced and consequences for infection and for receptor binding were measured. Receptor binding was measured initially by a sensitive assay based on coexpression of receptor and RBD inXenopus oocytes, and the findings were confirmed by using purified proteins. Three residues that are critical for both binding and infection (S84, D86, and W102), with side chains that extend into the pocket, were identified. Moreover, when mCAT-1 was overexpressed, the infectivity of Fr57-MLV carrying pocket substitutions was partially restored. Substitutions for 18 adjacent residues and 11 other previously unexamined surface-exposed residues outside of the RBD pocket had no detectable effect on function. Taken together, these findings support a model in which the RBD pocket interacts directly with mCAT-1 (likely residues, Y235 and E237) and multiple receptor-envelope complexes are required to form the fusion pore.

Mutational Analysis of the Putative Receptor-Binding Domain of Moloney Murine Leukemia Virus Glycoprotein gp70

“…The fact that all mutants involving amino acid W100 significantly reduced or abolished viral infectivity provides evidence for this hypothesis. Recently Davey et al (1999) have shown that W102 in Friend MuLV gp70 plays an important role in receptor interaction that further substantiates our result regarding the important role of W100 in Moloney gp70. From the above data, we would like to propose that the process of binding might not be a limiting factor for achieving wild-type titers in our functional assays.…”

A Hydrophobic Patch in Ecotropic Murine Leukemia Virus Envelope Protein Is the Putative Binding Site for a Critical Tyrosine Residue on the Cellular Receptor

“…These analyses of the receptor indicated that the virus glycoprotein-receptor interaction consists of multiple contacts, suggesting that it involves a more extensive site on SU than the serine, aspartate, and tryptophan residues provide. More importantly, no evidence for a direct interaction between any of these three SU residues and tyrosine 235 or glutamic acid 237 was reported by Davey and coworkers (5). We propose instead that aspartate 84 on Mo MLV (aspartate 86 on Friend 57 MLV) interacts with a critical receptor residue(s) other than tyrosine 235, perhaps with asparagine 232 and valine 233, lysine 234, or possibly glutamic acid 237.…”

“…Davey, Zuo, and Cunningham recently proposed that serine 84, aspartate 86, and tryptophan 102 in Friend MLV (corresponding to serine 82, aspartate 84, and tryptophan 100 in Mo MLV) form the core of the binding site for both tyrosine 235 and glutamic acid 237 on the receptor (5). They based this proposal on three points: first, that binding and infection were reduced by certain changes in these residues (5,13); second, that the three residues were adjacent on the surface of folded SU (7); and third, that the only critical receptor residues were tyrosine 235 and glutamic acid 237, from which erroneous assumption they concluded that any receptor binding site found on SU must be the site for these residues. However, Albritton and coworkers and Yoshimoto and coworkers had previously shown that at least two more receptor residues, asparagine 232 and valine 233, are involved in infection (1,18).…”

Substitutions of conserved amino acids in the receptor-binding domain of the spike glycoprotein affect utilization of murine CEACAM1a by the murine coronavirus MHV-A59

“…Alternatively, the high level of receptor expression on BHK + mCEACAM1a(I41R) cells may facilitate the recovery of these crippled viruses by increasing the number of receptors available on cell membranes. In a similar manner, increased expression of its cellular receptor partially restores the infectivity of a Friend murine leukemia virus with aa substitutions in its receptor binding pocket (Davey et al, 1999). In addition, the I41R substitution in the Nterminal domain of mCEACAM1a may facilitate the recovery of crippled viruses with mutant S proteins.…”