Mouse monoclonal antibody 5-21-3 recognizes a contiguous, conformation-dependent epitope and maps to a hydrophilic region in HIV-1 gp41.

Mouse monoclonal antibody 5-21-3 is mapped to an epitope within a hydrophilic region of HIV-1 gp41 between amino acids 642 and 665 (numbering by Meyers et al. based on HXB2 isolate). The epitope is formed from amino acids within the sequence IHSLIEESQNQQEKNEQELLELDK; however, antibody 5-21-3 is unable to recognize the epitope-forming sequence when it is presented to the antibody in the form of a short (642-665) synthetic polypeptide. The epitope apparently is partially formed when additional native sequence of varying length is added to the amino and/or carboxy ends of the epitope-forming sequence, and 5-21-3 binds these larger synthetic polypeptides to varying degrees depending on the position and length of the flanking sequences. The 5-21-3 epitope apparently is formed from contiguous amino acids which require a specific, conformation-dependent, secondary structure for proper epitope formation. Binding preferences exhibited by 5-21-3 toward synthetic polypeptides and recombinant proteins may reflect the conformational nature of the epitope in disrupted HIV which elicited formation of the monoclonal.