4AAL

MacA wild-type oxidized

Summary for 4AAL

• Entry DOI: 10.2210/pdb4aal/pdb
• Related: 4AAM 4AAN 4AAO
• Descriptor: CYTOCHROME C551 PEROXIDASE, HEME C, CALCIUM ION, ... (7 entities in total)
• Functional Keywords: oxidoreductase, multiheme cytochromes, conformational rearrangement
• Biological source: GEOBACTER SULFURREDUCENS
• Total number of polymer chains: 2
• Total formula weight: 78768.53

Authors

Seidel, J. (deposition date: 2011-12-05, release date: 2012-10-17, Last modification date: 2024-10-23)

Primary citation

Seidel, J.,Hoffmann, M.,Ellis, K.E.,Seidel, A.,Spatzal, T.,Gerhardt, S.,Elliott, S.J.,Einsle, O.
Maca is a Second Cytochrome C Peroxidase of Geobacter Sulfurreducens.
Biochemistry, 51:2747-, 2012

PubMed Abstract: The metal-reducing δ-proteobacterium Geobacter sulfurreducens produces a large number of c-type cytochromes, many of which have been implicated in the transfer of electrons to insoluble metal oxides. Among these, the dihemic MacA was assigned a central role. Here we have produced G. sulfurreducens MacA by recombinant expression in Escherichia coli and have solved its three-dimensional structure in three different oxidation states. Sequence comparisons group MacA into the family of diheme cytochrome c peroxidases, and the protein indeed showed hydrogen peroxide reductase activity with ABTS(-2) as an electron donor. The observed K(M) was 38.5 ± 3.7 μM H(2)O(2) and v(max) was 0.78 ± 0.03 μmol of H(2)O(2)·min(-1)·mg(-1), resulting in a turnover number k(cat) = 0.46 · s(-1). In contrast, no Fe(III) reductase activity was observed. MacA was found to display electrochemical properties similar to other bacterial diheme peroxidases, in addition to the ability to electrochemically mediate electron transfer to the soluble cytochrome PpcA. Differences in activity between CcpA and MacA can be rationalized with structural variations in one of the three loop regions, loop 2, that undergoes conformational changes during reductive activation of the enzyme. This loop is adjacent to the active site heme and forms an open loop structure rather than a more rigid helix as in CcpA. For the activation of the protein, the loop has to displace the distal ligand to the active site heme, H93, in loop 1. A H93G variant showed an unexpected formation of a helix in loop 2 and disorder in loop 1, while a M297H variant that altered the properties of the electron transfer heme abolished reductive activation.

PubMed: 22417533
DOI: 10.1021/BI300249U

Experimental method

X-RAY DIFFRACTION (1.84 Å)