HemQ: An iron-coproporphyrin oxidative decarboxylase for protoheme synthesis in Firmicutes and Actinobacteria

Genes for chlorite dismutase-like proteins are found widely among heme-synthesizing bacteria and some Archaea. It is now known that among the Firmicutes and Actinobacteria these proteins do not possess chlorite dismutase activity but instead are essential for heme synthesis. These proteins, named HemQ, are iron-coproporphyrin (coproheme) decarboxylases that catalyze the oxidative decarboxylation of coproheme III into protoheme IX. As purified, HemQs do not contain bound heme, but readily bind exogeneously supplied heme with low micromolar affinity. The heme-bound form of HemQ has low peroxidase activity and in the presence of peroxide the bound heme may be destroyed. Thus, it is possible that HemQ may serve a dual role as a decarboxylase in heme biosynthesis and a regulatory protein in heme homeostasis.