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.