Molecular evolution of the CYTH superfamily of proteins

Molecular evolution of the CYTH superfamily of proteins
L. Bettendorff, D. Delvaux, G. Kohn, P. Wins, B. Lakaye
GIGA-Neurosciences, University of Liège, Belgium
The CYTH superfamily of proteins was named after the two founding members, the CYaB adenylyl cyclase from Aeromonas hydrophila and the human 25-kDa THiamine triphosphatase (ThTPase). Members of this superfamily of proteins exist in all organisms including bacteria, archaea, plants and animals (except in birds) and can be traced back to the Last Universal Common Ancestor. They are characterized by a consensus sequence including several charged residues involved in divalent cation and triphosphate binding. Indeed, all members of the CYTH family that are characterized act on triphosphate derivatives and require at least one divalent cation for catalysis. The Nitrosomonas europaea (1) and E.coli CYTH proteins are specific inorganic triphosphatases. We propose that inorganic triphosphate (PPPi), the most simple triphosphate compound that can be imagined, is the primitive substrate of CYTH proteins. Other enzyme activities such as adenylate cyclase (in A. hydrophila), mRNA triphosphatase (in fungi and protozoans) and ThTPase (in metazoans) activities are secondary acquisitions. We show that ThTPase activity is not limited to mammals, but Sea anemone and Zebrafish CYTH proteins are already specific ThTPases and the acquisition of this enzyme activity is linked to the presence of a Trp (W53 in mammalian ThTPases) residue involved in the binding of the thiazole heterocycle of the thiamine molecule. The importance of W53 for the specificity of mammalian ThTPases is confirmed by site-directed mutagenesis. Furthermore, we propose a conserved catalytic mechanism between inorganic triphosphatases and ThTPases, based on a catalytic dyad comprising a Lys and a Tyr residue, explaining the alkaline pH optimum of CYTH proteins.

(1) Delvaux et al. J. Biol. Chem 286 (2011) 34023-35