A skewed distribution of amino acids at recognition sites of the hypervariable region of immunoglobulins.

Antibody binding site are formed by six hypervariable regions or complementarity determining regions (CDRs). The CDRs, three from the heavy chain and three from the light chain, are known as hypervariable segments and provide a surface complementary to that of the epitope. In recent work it was found that the amino acids in these positions fulfill different functions: Some play a structural role and others are involved in the specificity-determining function. It is reported here that the frequency of amino acids at hypervariable sites is skewed. By means of an informational algorithm, key physicochemical attributes of the dominant residues were identified for some of those sites. The results for about 1,500 antibodies suggest that approximately 35% of sites involved in the recognition process require only general properties such as composition, volume, and bulk or hydrogen bonding which are satisfied by a small set of amino acids instead of any one particular complementary amino acid.