[Somatic hypermutagenesis in immunoglobulin genes. II. Properties of somatic mutations and clonal selection]

Analysis of the collection of 203 somatic mutations in immunoglobulin genes was carried out. It was shown, that the high frequency of these mutations in CDRs of V-genes may be connected with the high concentration of repeats in these regions. In addition, the observed clusterization of mutations may emerge from simultaneous correction of several pertubations of complementarity in the heteroduplex, formed by the repeat regions. It was revealed, that somatic mutations in FRs are characterized by reliably smaller changes of some important amino acid physical-chemical properties than in CDRs. These data obviously indicate the occurrence of B-lymphocytes clonal selection. Analysis of synonymous substitutions has shown, that stabilizing selection seems to provide the conservatism of FRs (it leads to the conservation of the protein three-dimensional structure) and movement selection may provide the proliferation of B-lymphocytes with considerable changes in CDRs, if these mutations improve antigens binding. Preferential fixation of transitions in comparison with transversions, particularly expressed in FRs, may also be connected with the fact, that transitions lead to smaller changes of amino acid physical-chemical properties and they are rejected by selection to a smaller extent.