The crystal structure of the extracellular 11-heme cytochrome UndA reveals a conserved 10-heme motif and defined binding site for soluble iron chelates.
Members of the genus Shewanella translocate deca- or 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 UndA-Fe(III)-chelate complexes provides a rationale for previous kinetic measurements on UndA and other outer membrane cytochromes.
Centre for Molecular and Structural Biochemistry, School of Biological Sciences and School of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK.
Marcus J
MJ
Edwards
Andrea
A
Hall
Liang
L
Shi
James K
JK
Fredrickson
John M
JM
Zachara
Julea N
JN
Butt
David J
DJ
Richardson
Thomas A
TA
Clarke
D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D003580:Cytochromes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D005290:Ferric Compounds / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D007502:Iron Chelating Agents / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009571:Nitrilotriacetic Acid / Q000031:analogs & derivatives* / Q000737:chemistry; D010957:Plasmids; D011485:Protein Binding; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D020592:Shewanella / Q000737:chemistry* / Q000201:enzymology / Q000235:genetics; D012995:Solubility; D014169:Transformation, Bacterial
D001425:Bacterial Outer Membrane Proteins; D003580:Cytochromes; D005290:Ferric Compounds; D007502:Iron Chelating Agents; D006418:Heme; C025314:ferric citrate; D009571:Nitrilotriacetic Acid; C020326:ferric nitrilotriacetate