The amidohydrolase superfamily of enzymes has been divided into 24 clusters of orthologous groups (COG).  A large, divergent group of enzymes from cog0402, related to S-adenosylhomocysteine deaminase (SAH) (Tm0936) was found to house new enzymatic activities centered around adenosine deaminase.  Protein sequences from this group were retrieved from NCBI and a sequence similarity network diagram was constructed which revealed 13 major subgroups at an E-value cutoff of 10-110.  The active site residues were identified by comparison with the crystal structure of Tm0936 from Thermotoga maritima liganded with S-inosylhomocysteine (PDB: 2PLM).  Sequence alignments of the entire group were constructed and each subgroup displayed its own variation of active site residues, which differed primarily near the 5'-end of the ribose moiety, although 3 subgroups had more drastic modifications.  Proteins from each subgroup were purified and screened against a library of 5'-modified adenosine compounds.  New functions and substrate profiles were discovered, including 5'-deoxyadenosine deaminase from Desulfovibrio vulgaris (Dvu1825, kcat/Km = 1.2 x 107 M-1s-1), a new isoform of guanine deaminase from Moorella thermoacetica (Moth_1224, kcat/Km = 1.2 x 105 M-1s-1), and a promiscuous adenosine/5'-deoxy-5'-methylthioadenosine/SAH deaminase from Chromobacterium violaceum (Cv_1032).  Most enzymes purified for this investigation were found to have promiscuous activities, showing flexibility near the ribose 5'-binding pocket.  The compounds 5'-chloro-5'-deoxyadenosine and S-adenosylthiopropylamine were also deaminated.  In this group of enzymes from cog0402 there are at least 13 subgroups which carry their own unique substrate profiles.

Deamination of 5'-modified adenosines

244th National Meeting (2012)

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