Cytidine deaminase (EC 3.5.4.5) (cytidine aminohydrolase) catalyzes the hydrolysis of cytidine into uridine and ammonia while deoxycytidylate deaminase (EC 3.5.4.12) (dCMP deaminase) hydrolyzes dCMP into dUMP. Both enzymes are known to bind zinc and to require it for their catalytic activity [1,2]. The deaminases possess either one or two conserved zinc-coordinating (Z) motifs, with the consensus amino acid signature H-x(1)-E-x(24,28)-P-C-x(2,4)-C. This motif is required for catalytic activity. Zinc coordination is mediated by a histidine and two cysteines [3]. The CMP/dCMP-type deaminase domain consists of a central β-sheet with one or more α helices on each side (see <PDB:1JTK>) [4].

Such a region is also found in other proteins [3,4,5,6]:

• Yeast cytosine deaminase (EC 3.5.4.1) (gene FCY1) which transforms cytosine into uracil.
• Mammalian apolipoprotein B mRNA editing protein, responsible for the postranscriptional editing of a CAA codon into a UAA (stop) codon in the APOB mRNA.
• Riboflavin biosynthesis protein ribG, which converts 2,5-diamino-6- (ribosylamino)-4(3H)-pyrimidinone 5'-phosphate into 5-amino-6- (ribosylamino)-2,4(1H,3H)-pyrimidinedione 5'-phosphate.
• Bacillus cereus blasticidin-S deaminase (EC 3.5.4.23), which catalyzes the deamination of the cytosine moiety of the antibiotics blasticidin S, cytomycin and acetylblasticidin S.
• Bacillus subtilis protein comEB. This protein is required for the binding and uptake of transforming DNA.
• Bacillus subtilis tRNA-specific adenosine deaminase (tadA), catalyzes the deamination of adenosine to inosine at the wobble position of tRNAs.
• Escherichia coli tRNA-specific adenosine deaminase (tadA), catalyzes the deamination of adenosine to inosine at the wobble position of tRNAs.
• Yeast tRNA-specific adenosine deaminase subunit TAD2, deaminates adenosine- 34 to inosine in many tRNAs.

We have derived a signature pattern for this zinc-binding region. We also developed a profile which covers the entire CMP/dCMP-type deaminase domain.