Amino acid residues at conservative sites in proteins.

In the process of protein evolution, amino acid residues at certain sites are fixed by natural selection, indicating that such residues are important structurally and functionally. Analysis has revealed some useful observations concerning their specificity contributions. Physicochemical and conformational characteristics of amino acid residues do not seem to fully explain their occurrence probability at the conservative sites. The relative preferences of residues at these sites could be important in the control of biochemical specificity.