Idiotope structure and genetic diversity in anti-streptococcal group A carbohydrate antibodies.
Three cross-reactive idiotopes(Id), termed IdX, IdI-1, and Id5, that are present on free L chains from murine anti-group A streptococcal carbohydrate antibodies have been mapped; these Id distinguish between products of three homologous V kappa genes. For each determinant, sequence analysis of anti-streptococcal group A carbohydrate antibody V domains yielded small numbers of amino acids invariably associated with Id expression. Flow micro-fluorimetry was used to isolate three IdI-1- spontaneous mutants of the IdI-1+ hybridoma GAC 39; all had single amino acid changes in the L chain at position 60 and 77, all retained other Id, and all bound group A carbohydrate. Computer modeling was used to examine spatial relationships between Id. A number of the conserved Id5 and IdX residues cluster in the L chain framework region 1 around the first back loop connecting strands of the beta pleated sheets, and overlap at residue 15 (Id5, proline; IdX, leucine). This overlap accords with the mutually exclusive expression of Id5 and IdX. The IdI-1 loss variants have mutations of residues 60 or 77 on adjacent back loops, approximately 7.5 and 14 A from residue 15. Competitive inhibition of anti-IdX and anti-IdI-1 binding to antibodies expressing both Id can be attributed to steric hindrance. The framework back loops may be favored sites for cross-reactive Id expressed by products of a single V region gene. IdI-3a, an individual Id not associated with use of a particular gene segment, has been localized in part to residue 31 (hypervariable region 1) of the H chain.
Phillips
N J
NJ
Department of Pathology, Washington University School of Medicine, St. Louis, MO 63110.
Davie
J M
JM
D000595:Amino Acid Sequence; D000818:Animals; D000907:Antibodies, Bacterial / Q000032:analysis*; D002241:Carbohydrates / Q000276:immunology*; D014644:Genetic Variation; D007130:Immunoglobulin Idiotypes / Q000032:analysis*; D007147:Immunoglobulin Light Chains / Q000032:analysis; D051379:Mice; D008969:Molecular Sequence Data; D013297:Streptococcus pyogenes / Q000276:immunology*
D000907:Antibodies, Bacterial; D002241:Carbohydrates; D007130:Immunoglobulin Idiotypes; D007147:Immunoglobulin Light Chains