ANTIBODY-ANTIGEN RECOGNITION - A CANONICAL STRUCTURE PARADIGM

The antibodies of known three-dimensional structure exhibit a definite number of conformations (canonical structures) for five of six hyperv ariable loops, in the present study it was found that approximately 85 % of the immunoglobulin sequences analyzed fall into a small number of canonical structure combinations, representing only 3% of the total p ossible. These structures were classified into six distinct groups, de pending on the type of antigen with which they interact. Within each l oop, the positions responsible for maintaining these canonical structu res show a use frequency of amino acids that fits an inverse power law , whereas the use frequency of the amino acids responsible for the det ailed antigenic specificity follows an exponential distribution. We pr opose an evolutionary interpretation that connects these data, using t he fact that the inverse power law is generated by statistical process es of the type that yield a wealth curve and the fact that exponential distribution is generated by processes that are not biased by past hi story.