Purification and characterization of OmcZ, an outer-surface, octaheme c-type cytochrome essential for optimal current production by Geobacter sulfurreducens.

TitlePurification and characterization of OmcZ, an outer-surface, octaheme c-type cytochrome essential for optimal current production by Geobacter sulfurreducens.
Publication TypeJournal Article
Year of Publication2010
AuthorsInoue K, Qian X, Morgado L, Kim B-C, Mester T, Izallalen M, Salgueiro CA, Lovley DR
JournalAppl Environ Microbiol
Volume76
Issue12
Pagination3999-4007
Date Published2010 Jun
ISSN1098-5336
KeywordsBinding Sites, Bioelectric Energy Sources, Cytochromes c, Electricity, Electron Transport, Geobacter, Heme, Hot Temperature, Molecular Sequence Data, Molecular Weight, Oxidation-Reduction, Protein Binding, Protein Stability, Sequence Alignment, Sequence Analysis, Protein
Abstract

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.

DOI10.1128/AEM.00027-10
Alternate JournalAppl. Environ. Microbiol.
PubMed ID20400562