Compact archaeal variant of heme A synthase

The N- and C-terminal halves of the heme A synthase polypeptide of Bacillus subtilis, and many other organisms, are homologous. This indicates that these enzyme proteins originate from a tandem duplication and fusion event of a gene encoding a protein half as large. The ape1694 gene of the hyperthermophilic archaeon Aeropyrum pernix encodes a protein that is similar to the hypothetical small primordial protein. We demonstrate that this A. pernix protein is a heat-stable membrane bound heme A synthase designated cCtaA. The case of cCtaA is unusual in evolution in that the primordial-like protein has not become extinct and apparently carries out the same function as the twice as large more diversified heme A synthase protein variant found in most cytochrome a-containing organisms.