MASKING OF RETROVIRAL ENVELOPE FUNCTIONS BY OLIGOMERIZING POLYPEPTIDEADAPTERS

We have constructed chimeric retroviral envelopes displaying N-termina l polypeptides that are known to form homotrimeric associations. The a mphotropic receptor (RAM-I) binding domain from the trimeric surface ( SU) glycoprotein of 4070A murine leukemia virus (MLV)-inhibited ecotro pic receptor (Rec-1) mediated infection by the SU glycoprotein of Molo ney MLV when grafted to its N-terminus. The block to Rec-l-mediated in fection was reversed when the RAM-I binding domain was cleaved from th e vector particles using an engineered factor Xa protease-sensitive cl eavage signal between the envelope glycoprotein and its N-terminal ext ension. Trimeric leucine zipper peptides and the trimeric C-terminal d omain of CD40 ligand were shown to inhibit RAM-I-mediated infection of NIH313 cells by the 4070A envelope when fused to its N-terminus, wher eas monomeric helical peptides and the monomeric epidermal growth fact or domain did not. The block to RAM-I-mediated infection was reversed when the trimeric polypeptides were cleaved from the Vector particles by addition of factor Xa protease. Envelope binding assays using cleav ed and uncleaved chimeric 4070A envelopes revealed that binding to RAM -1 receptors on mammalian cells was hindered by trimeric, but not by m onomeric, N-terminal polypeptides. These results have important implic ations for the design of protease-activatable vectors for targeted gen e delivery. (C) 1997 Academic Press.