Fe(II) cytochrome c551 from the organism Pseudomonas aeruginosa is a heme-binding protein. The protein binds one heme group per molecule, and it is located in the periplasm. Biologically, this protein functions as an electron donor for cytochrome cd1 in nitrite and nitrate respiration. Its redox potential is +260 mv.
Fe(II) Cytochrome c551 is an 82 amino acid residue protein and contains no disulfide bonds. Regarding secondary structure, this protein contains 5 alpha helices. The 4 colored gold are right-handed helices, but the one colored blue is a 310 alpha helix. A heme molecule is also shown associated with the protein. In the cytochrome c family, heme is bound to the molecule via two conserved cysteine residues. The amino acid sequence for this binding site is Cys-X-X-Cys-His. In cytochrome c551, the sequence reads Cys-Val-Ala-Cys-His. The two cysteines are residues 12 and 15.