Purification and characterization of OmcZ, an outer-surface, octaheme c-type cytochrome essential for optimal current production by Geobacter sulfurreducens.
Previous studies have demonstrated that Geobacter sulfurreducens requires the c-type cytochrome OmcZ, which is present in large (OmcZ(L); 50-kDa) and small (OmcZ(S); 30-kDa) forms, for optimal current production in microbial fuel cells. This protein was further characterized to aid in understanding its role in current production. Subcellular-localization studies suggested that OmcZ(S) was the predominant extracellular form of OmcZ. N- and C-terminal amino acid sequence analysis of purified OmcZ(S) and molecular weight measurements indicated that OmcZ(S) is a cleaved product of OmcZ(L) retaining all 8 hemes, including 1 heme with the unusual c-type heme-binding motif CX(14)CH. The purified OmcZ(S) was remarkably thermally stable (thermal-denaturing temperature, 94.2 degrees C). Redox titration analysis revealed that the midpoint reduction potential of OmcZ(S) is approximately -220 mV (versus the standard hydrogen electrode [SHE]) with nonequivalent heme groups that cover a large reduction potential range (-420 to -60 mV). OmcZ(S) transferred electrons in vitro to a diversity of potential extracellular electron acceptors, such as Fe(III) citrate, U(VI), Cr(VI), Au(III), Mn(IV) oxide, and the humic substance analogue anthraquinone-2,6-disulfonate, but not Fe(III) oxide. The biochemical properties and extracellular localization of OmcZ suggest that it is well suited for promoting electron transfer in current-producing biofilms of G. sulfurreducens.
Inoue
Kengo
K
Department of Microbiology, University of Massachusetts, 639 North Pleasant St., Amherst, MA 01003, USA. kinoue@microbio.umass.edu
Qian
Xinlei
X
Morgado
Leonor
L
Kim
Byoung-Chan
BC
Mester
Tünde
T
Izallalen
Mounir
M
Salgueiro
Carlos A
CA
Lovley
Derek R
DR
D001665:Binding Sites; D001674:Bioelectric Energy Sources; D045304:Cytochromes c / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism*; D004560:Electricity; D004579:Electron Transport; D045302:Geobacter / Q000201:enzymology* / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D006358:Hot Temperature; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010084:Oxidation-Reduction; D011485:Protein Binding; D055550:Protein Stability; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein
D006418:Heme; D045304:Cytochromes c
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