CHARACTERIZATION OF V3 LOOP-BINDING PROTEIN(S) OF MOLT-4 AND U937 CELLS

The V3 loop in gp120 of human immunodeficiency virus type 1 (HIV-1) is known as a principal neutralizing and cell-tropic determinant, Biotin ylated synthetic V3 loop peptides derived from three different HIV-1 s trains were used as ligands to identify the cell surface counterrecept or, which may participate in the infection of HIV-1. Two different cel l lines, Molt-4 and U937, and three V3 loop peptides derived from LAV( ELI), HTLV-IIIMN, and HTLV-IIIB strains were used. The binding of HTLV -IIIB-derived peptide to the cell surface was confirmed using I-125-la beled surface proteins of both cell lines. The relative molecular mass of the major radioactive band on the autoradiogram was 32-33 kDa in b oth cell lines. A protein was purified from the plasma membrane fracti on of Molt-4 cells using affinity columns coupled with three different V3 loop peptides, Two major polypeptides (32 and 33 kDa) were eluted from the affinity column, Size-exclusion chromatography showed that th e protein migrated as a single peak with a molecular mass of 130 kDa. These proteins were separated by reversed-phase chromatography, which indicated that the 32-kDa protein is more hydrophobic than the 33-kDa protein in Molt-4 cells, A similar but not identical 130-kDa protein w ith 32- and 33-kDa polypeptides were also purified from U937 cells, Th ese findings indicate that HIV-1 utilizes a tetrameric protein on the surface of Molt-4 and U937 cells on infection.