Cloning and sequence analysis of the gene encoding Methylophilus methylotrophus cytochrome c '', a unique protein with a perpendicular orientation ofthe histidinyl ligands

Cytochrome c " from Methylophilus methylotrophus is an unusual monohaem pro tein that undergoes a major redox-linked spin-state transition: one of the two axial histidines bound to the iron in the oxidised form is detached upo n reduction-and a proton is taken up. A 3.5-kb DNA fragment, containing the gene encoding cytochrome c " (cycA), has been cloned and sequenced. The cy tochrome c " gene codes for a pre-protein with a typical prokaryotic 20-res idue signal sequence, suggesting that the protein is synthesised as a precu rsor which is processed during its secretion into the periplasm. The C-term inus of cytochrome c " has homology with the corresponding region of an oxy gen-binding haem protein (SHP) from phototrophically grown Rhodobacter spha eroides. SHP is similar in size and in the location of its haem-binding sit e. Immediately downstream from cytochrome c " a second open reading frame ( ORF) codes for a 23-kDa protein with similarity to the cytochrome b-type su bunit of Ni-Fe hydrogenase. The possibility of coordinated expression of cy cA and this ORF is discussed. (C) 1999 Elsevier Science B.V. All rights res erved.