Bacillus subtilis CtaA is a hemecontaining membrane protein involved in heme A biosynthesis

Heme A is a prosthetic group of many respiratory oxidases. It is synthesized from protoheme IX (heme B) seemingly with heme 0 as a stable intermediate. The Bacilus subtilis ctaA and ctaB genes are required for heme A and heme 0 synthesis, respectively (B. Svensson, M. Lubben, and L. Hederstedt, Mol. Microbiol. 10:193-201, 1993). Tentatively, CtaA is involved in the monooxygenation and oxidation of the methyl side group on porphyrin ring D in heme A synthesis from heme B. B. subtilis ctaA and ctaB on plasmids in both B. subtilis and Escherichia coil were found to result in a novel membrane-bound heme-containing protein with the characteristics of a low-spin b-type cytochrome. It can be reduced via the respiratory chain, and in the reduced state it shows light absorption maxima at 428, 528, and 558 nm and the a-band is split. Purified cytochrome isolated from both B. subtilis and E. coli membranes contained one polypeptide identified as CtaA by amino acid sequence analysis, about 0.2 mol of heme B per mol of polypeptide, and small amounts of heme A. The gram-positive aerobic soil bacterium Bacillus subtilis can synthesize a-, b-, c-, d-, and o-type cytochromes (41), which contain heme A, protoheme IX (heme B), heme C, heme D, and heme 0, respectively. Four different terminal oxidases have been found in B. subtilis: two aa3-type cytochromes (th