The structural basis of antigenic determinants on V kappa 21 light chains

Antisera were raised against L chains of the V_κ21 group. These antisera divide the six structurally defined subgroups of V_κ21 into two serogroups. The residues thought to comprise the Serogroup I and Serogroup II determinants were located by comparing the complete V region sequences in Serogroup I(16 proteins) and Serogroup II (8 proteins) to each other and to non-V_κ21 chains. The positions implicated in the V_κ21 serogroup specificities were position 34 in Ll and positions 72, 78 and 84 in FR3. The Serogroup I specificity may be associated with Glu 84. The Serogroup II specificity may be associated with Thr 78 and Ala 84. Asn 34 cannot be ruled out completely. The extent to which certain serogroup-associated residues contribute to the V_κ21 antigenic determinants was assessed by constructing molecular models of V region domains. These demonstrated that the side-chains at positions 78 and 84 were close to the surface of the molecule, and suggested that the shape of these side-chains might not be the major factor in forming the serogroup specificities. Consequently, serogroup-associated residues seem to contribute either individually or in certain combinations to the determinants(s).