Mutational, crystallographic and phylogenetic analysis of nucleotidyl cyclases have been used to understand how these enzymes discriminate between substrates. Ma1120, a class III adenylyl cyclase (AC) from Mycobacterium avium, was used as a model to study the amino acid residues that determine substrate preference, by systematically replacing ATP specifying residues with those known to specify GTP. This enzyme was found to possess residual guanylyl cyclase (GC) activity at alkaline pH. Replacement of key residues lysine (101) and aspartate (157) with residues conserved across GCs by site directed mutagenesis, led to a marked improvement in GC activity and a decrease in AC activity. This could be correlated to the presence and strength of the hydrogen bond between the second substrate binding residue (157) and the base of the nucleotide triphosphate. This is substantiated by the fact that the pH optimum is highly dependent on the amino acid residues present at positions 101 and 157.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.