Functional dissection of the Moloney murine leukemia virus envelope protein gp70

The envelope protein of Moloney murine leukemia virus (Mo-MLV) is a complex glycoprotein that mediates receptor binding and entry via fusion with cell membranes. By using a series of substitution mutations and truncations in the Mo-MLV external envelope surface protein gp70, we have identified regions important for these processes. Firstly, truncations of gp70 revealed that the minimal continuous receptor-binding region is amino acids 9 to 230, in broad agreement with other studies. Secondly, within this region there are two key basic amino acids, Arg-83 and Arg-95, that are essential for receptor binding and may interact with a negatively charged residue(s) or with the pi electrons of the aromatic ring on a hydrophobic residue(s) in the basic amino acid transporter protein that is the Mo-MLV ecotropic receptor. Finally, we showed that outside the minimal receptor-binding region at amino acids 2 to 8, there is a region that is essential for postbinding fusion events.