ENTRY OF AMPHOTROPIC MURINE LEUKEMIA-VIRUS IS INFLUENCED BY RESIDUES IN THE PUTATIVE 2ND EXTRACELLULAR DOMAIN OF ITS RECEPTOR, PIT2

Human cells express distinct but related receptors for the gibbon ape leukemia virus (GALV) and the amphotropic murine leukemia virus (A-MuL V), termed Pit1 and Pit2, respectively. Pit1 is not able to function a s a receptor for A-MuLV infection, while Pit2 does not confer suscepti bility to GALV. Previous studies of chimeric receptors constructed by interchanging regions of Pit1 and Pit2 failed to clarify the determina nts unique to Pit2 which correlate with A-MuLV: receptor function. In order to identify which regions of Pit2 are involved in A-MuLV recepto r function, we exchanged the putative second and third extracellular d omains of Pit1, either individually or together,,vith the correspondin g regions of Pit2, Our functional characterization of these receptors indicates a role for the putative second extracellular domain (domain II) in A-MuLV infection. We further investigated the influence of doma in LT with respect to A-MuLV: receptor function by performing site-spe cific mutagenesis within this region of Pit2, Many of the mutations ha d little or no effect on receptor function. However, the substitution of serine for methionine at position 138 (S138M) in a Pit1 chimera con taining domain II of Pit2 resulted in a 1,000-fold reduction in A-MuLV receptor function, Additional mutations made within domain II of the nonfunctional S138M mutant restored receptor function to nearly wild-t ype efficiency: The high degree of tolerance for mutations as well as the compensatory effect of particular substitutions observed within do main II suggests that an element of secondary structure within this re gion plays a critical role in the interaction of the receptor with A-M uLV.