Structural characterization of two tandemly arranged DNA methyltransferase genes from Neisseria gonorrhoeae MS11: N4-cytosine specific M.NgoMXV and nonfunctional 5-cytosine-type M.NgoMorf2P

Two adjacent genes encoding DNA methyltransferases (MTases) of Neisseria gonorrhoeae MS11, an active N4-cytosine specific M. NgoMXV and an inactive 5-cytosine type M. NgoMorf2P, were cloned into Escherichia coli and sequenced. We analyzed the deduced amino acid sequence of both gene products and localized conserved regions characteristic for DNA MTases. Structure prediction, threading-derived alignments, and comparison with the common fold for DNA MTases allowed for construction of super-secondary and tertiary models for M.NgoMorf2P and M.NgoMXV, respectively. These models helped in identification of amino acids and structural elements essential for function of both enzymes. The implications of this putative structural model on the catalytic mechanism of M.NgoMXV and its possible relation to the common ancestor of modern DNA amino-MTases are also discussed.