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

Abstract

In the receptor for ecotropic murine leukemia viruses, tyrosine 235 contributes a critical hydrophobic side chain to the virus-receptor interaction (14). Here we report that tryptophan 142 in ecotropic Moloney murine leukemia virus envelope protein is essential to virus binding and infection. Replacement of tryptophan 142 by alanine or serine resulted in misfolding. However, replacement by methionine (W142M) allowed correct folding of the majority of glycoprotein molecules. W142M virus showed a marked reduction in virus binding and was almost noninfectious, suggesting that tryptophan 142 is involved in receptor binding. In contrast, W142Y virus containing a replacement of tryptophan 142 with an aromatic residue (tyrosine) was as efficient as wild-type virus in infection and binding of cells expressing the wild-type receptor. However, W142Y virus was 100-fold less efficient than wild-type virus in infection of cells expressing a mutant receptor containing tryptophan instead of the critical tyrosine. These results strongly support tryptophan 142 being an essential residue on the virus envelope protein that interacts directly with the critical hydrophobic residue at position 235 of the ecotropic receptor. Tryptophan 142 forms one side of a shallow hydrophobic pocket on the surface of the envelope protein, suggesting that it might comprise the complete putative binding site for tyrosine 235. We discuss the implications of our findings with respect to two models of the envelope protein trimer. Interestingly, both models place tryptophan 142 at the interface between adjacent subunits of the trimer.

Turning of the receptor-binding domains opens up the murine leukaemia virus Env for membrane fusion

“…In one model, the RBDs were arranged with the backs of the heads interacting with each other at the three-fold axis, that is, in the opposite orientation as in our model of native Env ( Fass, 1997 ). In the other model, the RBDs were arranged similar to the organization in our IAS Env, although without gaps between the monomers ( Zavorotinskaya and Albritton, 1999 ). The interesting feature with the latter model was that it colocalized the front receptor-binding site of one monomer with the back site of another one.…”

“…It is an L-shaped molecule and consists of an antiparallel β-sandwich and a helical subdomain. Because the Mo- and F-RBD have 89% amino-acid sequence identity and 97% conservation, we used the atomic structure of F-RBD to model the corresponding Mo-RBD structure ( Zavorotinskaya and Albritton, 1999 ). Not surprisingly, the structure of the Mo-RBD looked almost identical to that of F-RBD.…”

“…The former unit is exposed on the upper-front part of the neck, projecting into the cavity of the trimer, and the latter on the left side of the neck, close to the base, projecting peripherally from the oligomer ( Figure 7 , native Env, side views). Two receptor-binding regions have been mapped on the Mo-RBD SU ( Yoshimoto et al , 1993 ; MacKrell et al , 1996 ; Bae et al , 1997 ; Davey et al , 1997 , 1999 ; Zavorotinskaya and Albritton, 1999 ). One (involving residues Arg83 and Asp84) was localized in the upper-front and the other (involving Trp142) in the upper-back part of the head (indicated by spheres in Figure 6 ).…”

“…The two receptor-binding regions that have been mapped in the RBD are exposed in the native Env trimer, the upper-front sites around the three-fold axis in the centre of the Env tip and the upper-back sites at the periphery of the tip ( Yoshimoto et al , 1993 ; MacKrell et al , 1996 ; Bae et al , 1997 ; Davey et al , 1997 , 1999 ; Zavorotinskaya and Albritton, 1999 ). The latter sites appear to be more easily accessible, at least for multiple receptors.…”

Novel Bifunctional Single-Chain Variable Antibody Fragments to Enhance Virolysis by Complement: Generation and Proof-of-Concept

“…Detailed information about mAb48 and its target (i.e., epitope mapping) for further analysis has not been done yet. The 48scFv binds distant from the main binding pocket and may also show reduced affinity compared to its parental antibody [47], since scFv usually exhibit reduced avidity due to their monovalent structure. Nevertheless, this in silico binding data stresses the potential of the SCR-modules and excludes neutralizing effects of the 48scFv-moiety of the scFv-SCR constructs.…”