The Crystal Structure of the Extracellular 11-heme CytochromeUndAReveals a Conserved 10-heme Motif and Defined Binding Site for Soluble Iron Chelates

Authors

• Marcus J. Edwards, University of East Anglia
• Andrea Hall, University of East Anglia
• Liang Shi, Pacific Northwest National LaboratoryFollow
• James K. Fredrickson, Pacific Northwest National LaboratoryFollow
• John M. Zachara, Pacific Northwest National LaboratoryFollow
• Julea N. Butt, University of East Anglia
• David J. Richardson, University of East AngliaFollow
• Thomas A. Clarke, University of East AngliaFollow

Date of this Version

2012

Citation

Structure 20, 1275–1284, July 3, 2012; DOI 10.1016/j.str.2012.04.016

Abstract

Members of the genus Shewanella translocate decaor undeca-heme cytochromes to the external cell surface thus enabling respiration using extracellular minerals and polynuclear Fe(III) chelates. The high resolution structure of the first undeca-heme outer membrane cytochrome, UndA, reveals a crossed heme chain with four potential electron ingress/ egress sites arranged within four domains. Sequence and structural alignment of UndA and the deca-heme MtrF reveals the extra heme of UndA is inserted between MtrF hemes 6 and 7. The remaining UndA hemes can be superposed over the heme chain of the decaheme MtrF, suggesting that a ten heme core is conserved between outer membrane cytochromes. The UndA structure has also been crystallographically resolved in complex with substrates, an Fe(III)-nitrilotriacetate dimer or an Fe(III)-citrate trimer. The structural resolution of these UndAFe( III)-chelate complexes provides a rationale for previous kinetic measurements on UndA and other outer membrane cytochromes.