IN-VITRO BINDING OF PURIFIED MURINE ECOTROPIC RETROVIRUS ENVELOPE SURFACE PROTEIN TO ITS RECEPTOR, MCAT-1

An amino-terminal portion of the Friend murine leukemia virus (MLV) en velope surface protein {SU, residues 1 to 236 [SU:(1-236)]} and its re ceptor, MCAT-1, were each purified from insect cells after expression by using recombinant baculoviruses. Friend SU:(1-236) bound specifical ly to Xenopus oocytes that expressed MCAT-1 with an affinity (K-d, 55 nM) similar to that of viral SU binding to permissive cells, Direct bi nding of Friend SU:(1-236) to purified MCAT-1 was observed in detergen t and after reconstitution into liposomes. Analysis of binding demonst rated that MCAT-1 and Friend SU:(1-236) interact with a stoichiometry of near 1:1, These findings demonstrate that the amino-terminal domain from the SU of ecotropic murine retroviruses contains an MCAT-1 bindi ng domain.