cytochrome c
octaheme cytochrome
heme
octaheme cytochrome, a homotrimer with an unprecedented fold and heme arrangement, as well as a heme bound to a CX15CH motif. The heterobimetallic active-site heme 2 has a Cu(I) ion juxtaposed to a heme c at a Fe-Cu distance of 4.4 A, active-site heme 2 is bound to a canonical CXXCH motif with H306 as a proximal axial ligand. In the CX15CH motif of heme 8, the extended region between the two cysteine residues forms a loop with a short helical turn, in direct vicinity to another loop harbouring the only non-proline cis peptide in the enzyme, between residues G508 and F509. Its formation might require the essential peptidyl isomerase MccB2, and it is presumed to be a prerequisite for correct folding of the loop in the maturation process of heme 8, which is likely to be attached by the dedicated cytochrome c synthase CcsA1. The structure of the CX15CH heme c binding motif disrupts the general parallel/perpendicular heme stacking sequence, and rotates the heme out of plane, possibly to optimize the interaction with the putative electron donor, the iron-sulfur protein MccC
more
no activity is observed with NAD, NADP, FAD or FMN
siroheme
at least two of three subunits contain two pairs of [Fe4-S4]-centers and siroheme units
siroheme
binding of two sirohemes and four [4Fe-4S]-clusters per alpha2beta2 structure
siroheme
close to 80% of the siroheme moiety in the enzyme is demetallated
siroheme
cofactor is extensivel demetallated
siroheme
four sirohemes per enzyme molecule
siroheme
protein complex contains two siroheme-[4Fe4S] cofactors bound by subunit DsrB, two sirohydrochlorins and two [4Fe-4S]-centers bound by subunit DsrA, and another four [4Fe-4S]-centers in the ferredoxin domains
siroheme
protein contains high-spin siroheme
