title: EfeO-cupredoxins: major new members of the cupredoxin superfamily with roles in bacterial iron transport.
abstract: The EfeUOB system of Escherichia coli is a tripartite, low pH, ferrous iron transporter. It resembles the high-affinity iron transporter (Ftr1p-Fet3p) of yeast in that EfeU is homologous to Ftr1p, an integral-membrane iron-permease. However, EfeUOB lacks an equivalent of the Fet3p component--the multicopper oxidase with three cupredoxin-like domains. EfeO and EfeB are periplasmic but their precise roles are unclear. EfeO consists primarily of a C-terminal peptidase-M75 domain with a conserved 'HxxE' motif potentially involved in metal binding. The smaller N-terminal domain (EfeO-N) is predicted to be cupredoxin (Cup) like, suggesting a previously unrecognised similarity between EfeO and Fet3p. Our structural modelling of the E. coli EfeO Cup domain identifies two potential metal-binding sites. Site I is predicted to bind Cu(2+) using three conserved residues (C41 and 103, and E66) and M101. Of these, only one (C103) is conserved in classical cupredoxins where it also acts as a Cu ligand. Site II most probably binds Fe(3+) and consists of four well conserved surface Glu residues. Phylogenetic analysis indicates that the EfeO-Cup domains form a novel Cup family, designated the 'EfeO-Cup' family. Structural modelling of two other representative EfeO-Cup domains indicates that different subfamilies employ distinct ligand sets at their proposed metal-binding sites. The ~100 efeO homologues in the bacterial sequence databases are all associated with various iron-transport related genes indicating a common role for EfeO-Cup proteins in iron transport, supporting a new copper-iron connection in biology.
authors.affiliation: School of Biological Sciences, University of Reading, Whiteknights, Reading RG6 6AJ, UK.
authors.forename: Mohan B
authors.initials: MB
authors.lastname: Rajasekaran
authors.forename: Sanjay
authors.initials: S
authors.lastname: Nilapwar
authors.forename: Simon C
authors.initials: SC
authors.lastname: Andrews
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Watson
mesh_terms: D000595:Amino Acid Sequence; D001400:Azurin / Q000378:metabolism*; D001692:Biological Transport; D027682:Cation Transport Proteins / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D007501:Iron / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D016415:Sequence Alignment
chemical_list: D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; C050107:cupredoxin; C516304:efeU' protein, E coli; D001400:Azurin; D007501:Iron