Deciphering the distribution of quinone biosynthetic pathways across Proteobacteria

Coproheme decarboxylases (ChdCs) are enzymes responsible for the catalysis of the terminal step in the coproporphyrin-dependent heme biosynthesis pathway. Phylogenetic analyses confirm that the gene encoding for ChdCs is widespread throughout the bacterial world. It is found in monoderm bacteria (Firmicutes, Actinobacteria), diderm bacteria (e. g. Nitrospirae) and also in Archaea. In order to test phylogenetic prediction ChdC representatives from all clades were expressed and examined for their coproheme decarboxylase activity. Based on available biochemical data and phylogenetic analyses a sequence motif (-Y-P-M/F-X-K/R-) is defined for ChdCs. We show for the first time that in diderm bacteria an active coproheme decarboxylase is present and that the archaeal ChdC homolog from Sulfolobus solfataricus is inactive and its physiological role remains elusive. This shows the limitation of phylogenetic prediction of an enzymatic activity, since the identified sequence motif is equally conserved across all previously defined clades.