title: Apo and ligand-bound structures of ModA from the archaeon Methanosarcina acetivorans.
abstract: The trace-element oxyanion molybdate, which is required for the growth of many bacterial and archaeal species, is transported into the cell by an ATP-binding cassette (ABC) transporter superfamily uptake system called ModABC. ModABC consists of the ModA periplasmic solute-binding protein, the integral membrane-transport protein ModB and the ATP-binding and hydrolysis cassette protein ModC. In this study, X-ray crystal structures of ModA from the archaeon Methanosarcina acetivorans (MaModA) have been determined in the apoprotein conformation at 1.95 and 1.69 A resolution and in the molybdate-bound conformation at 2.25 and 2.45 A resolution. The overall domain structure of MaModA is similar to other ModA proteins in that it has a bilobal structure in which two mixed alpha/beta domains are linked by a hinge region. The apo MaModA is the first unliganded archaeal ModA structure to be determined: it exhibits a deep cleft between the two domains and confirms that upon binding ligand one domain is rotated towards the other by a hinge-bending motion, which is consistent with the 'Venus flytrap' model seen for bacterial-type periplasmic binding proteins. In contrast to the bacterial ModA structures, which have tetrahedral coordination of their metal substrates, molybdate-bound MaModA employs octahedral coordination of its substrate like other archaeal ModA proteins.
authors.affiliation: UCLA-DOE Institute for Genomics and Proteomics, University of California at Los Angeles, Los Angeles, CA 90095, USA.
authors.forename: Sum
authors.initials: S
authors.lastname: Chan
authors.forename: Iulia
authors.initials: I
authors.lastname: Giuroiu
authors.forename: Irina
authors.initials: I
authors.lastname: Chernishof
authors.forename: Michael R
authors.initials: MR
authors.lastname: Sawaya
authors.forename: Janet
authors.initials: J
authors.lastname: Chiang
authors.forename: Robert P
authors.initials: RP
authors.lastname: Gunsalus
authors.forename: Mark A
authors.initials: MA
authors.lastname: Arbing
authors.forename: L Jeanne
authors.initials: LJ
authors.lastname: Perry
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000378:metabolism; D000595:Amino Acid Sequence; D001059:Apoproteins / Q000737:chemistry* / Q000378:metabolism; D019843:Archaeal Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D018360:Crystallography, X-Ray; D008024:Ligands; D017020:Methanosarcina / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D013379:Substrate Specificity
chemical_list: D018528:ATP-Binding Cassette Transporters; D001059:Apoproteins; D019843:Archaeal Proteins; D008024:Ligands