IDENTIFICATION OF A SUBDOMAIN IN THE MOLONEY MURINE LEUKEMIA-VIRUS ENVELOPE PROTEIN INVOLVED IN RECEPTOR-BINDING

We have mutated amino acids within the receptor-binding domain of Molo ney murine leukemia virus envelope in order to identify residues invol ved in receptor binding, Analysis of mutations in the region of amino acids 81 to 88 indicates that this region is important for specific en velope-receptor interactions, None of the aspartate 84 (D-84) mutants studied bind measurably, although they are efficiently incorporated in to particles, D-84 mutants have titers that correspond to the severity of the substitution, This observation suggests that D-84 may provide a direct receptor contact, Mutations in the other charged amino acids in this domain (R-83, E-86, and E-87) yield titers similar to those of wild-type envelope, but the affinity of the mutant envelope in the bi nding assay is decreased by nonconservative substitutions in parallel to the severity of the change, These other amino acids may either prov ide secondary receptor contacts or assist in maintaining a structure i n the domain that favors efficient binding, We also studied other regi ons of high hydrophilicity. Our initial characterization indicates tha t amino acids 106 to 111 and 170 to 188 do not play a major role in re ceptor binding, Measurements of relative binding affinity and titer in dicate that most mutations in the region of amino acids 120 to 131 did not significantly affect receptor binding, However, SU encoded by mut ants H123V, R124L, and C131A as well as C81A could not be detected in particles and therefore did not bind measurably, Therefore, the region encompassed by amino acids 81 to 88 appears to be directly involved i n receptor binding.