Molecular analysis of human immunoglobulin heavy chain variable region associated determinants recognized by anti-VH3 antibodies 7B4, b6 and D12

7B4, B6 and D12 are murine monoclonal antibodies (MoAb) that bind to some h uman immunoglobulin heavy chain products of the closely related V3-30, V3-3 0.3 and V3-33 genes from the VH3 family. B6 and D12 have additional reactiv ities with some immunoglobulins (Ig) encoded by the V3-11 and V3-7 genes; D 12 also reacts with some V3-43 gene Ig. We show here, by site-directed muta gensis, that the lysine at position 57 in the complementarity-determining r egion 2 (CDR-2) of the V3-30 gene product is crucial for epitope recognitio n by all three anti-VH3 MoAbs. Further analysis of the amino-acid sequences of a large panel of Ig reactive, or nonreactive, with MoAb 7B4 indicates t hat the determinant recognized by 7B4 is dependent on the presence of the t etrapeptide sequence NKYY between positions 56 and 59 in the CDR-2. Compari ng the efficiency of 7B4 reactivity with VH3 gene-encoded human Ig indicate s that amino-acid position 4 in the frame region 1 (FR-1) may also influenc e the binding of 7B4 to Ig encoded by three very closely related germline g enes, V3-30, V3-30.3 and V3-33. NKYY is also found on the gp120 V3 region o f human immunodeficiency virus (HIV)-2, SIV and HTLV-4. We also report that other tetrapeptide sequences found on the 56-59 motif of heavy chain varia ble regions encoded by germline genes are expressed on the solvent exposed V2 region of gp120 of HIV-1 isolates. The possible significance of these ob servations is discussed.