STRUCTURE-BASED SEQUENCE ALIGNMENT OF 3 ADOMET-DEPENDENT DNA METHYLTRANSFERASES

M . HhaI, M . TaqI and COMT are DNA methyltransferases (MTases) which catalyze the transfer of a methyl group from the cofactor AdoMet to C5 of cytosine, to N6 of adenine and to a hydroxyl group of catechol, respectively. The larger catalytic domains of the bilobal proteins, M . HHaI and M . TaqI, and the entire single domain of COMT have an alp structure containing a mixed central beta-sheet. These domains havevery similar folding. By allowing appropriate 'insertions' or 'deletions' in the backbones of the three structures, it was possible to find more conserved motifs in M . TaqI and COMT. The similarity in protein folding and the equivalence of amino-acid sequences revealed by the structural alignment indicate that many AdoMet-dependent MTases may share a common catalytic domain structure.