title: Preliminary time-of-flight neutron diffraction studies of Escherichia coli ABC transport receptor phosphate-binding protein at the Protein Crystallography Station.
abstract: Inorganic phosphate is an essential molecule for all known life. Organisms have developed many mechanisms to ensure an adequate supply, even in low-phosphate conditions. In prokaryotes phosphate transport is instigated by the phosphate-binding protein (PBP), the initial receptor for the ATP-binding cassette (ABC) phosphate transporter. In the crystal structure of the PBP-phosphate complex, the phosphate is completely desolvated and sequestered in a deep cleft and is bound by 13 hydrogen bonds: 12 to protein NH and OH donor groups and one to a carboxylate acceptor group. The carboxylate plays a key recognition role by accepting a phosphate hydrogen. PBP phosphate affinity is relatively consistent across a broad pH range, indicating the capacity to bind monobasic (H2PO4-) and dibasic (HPO4(2-)) phosphate; however, the mechanism by which it might accommodate the second hydrogen of monobasic phosphate is unclear. To answer this question, neutron diffraction studies were initiated. Large single crystals with a volume of 8 mm3 were grown and subjected to hydrogen/deuterium exchange. A 2.5 Å resolution data set was collected on the Protein Crystallography Station at the Los Alamos Neutron Science Center. Initial refinement of the neutron data shows significant nuclear density, and refinement is ongoing. This is the first report of a neutron study from this superfamily.
authors.affiliation: Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
authors.forename: K H
authors.initials: KH
authors.lastname: Sippel
authors.affiliation: Bioscience Division B-11, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
authors.forename: J
authors.initials: J
authors.lastname: Bacik
authors.affiliation: Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
authors.forename: F A
authors.initials: FA
authors.lastname: Quiocho
authors.affiliation: Scientific Activities Division, European Spallation Source, 221 00 Lund, Sweden.
authors.forename: S Z
authors.initials: SZ
authors.lastname: Fisher
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry*; D018360:Crystallography, X-Ray / Q000295:instrumentation*; D029968:Escherichia coli Proteins / Q000737:chemistry*; D009502:Neutrons; D010710:Phosphates / Q000737:chemistry
chemical_list: D018528:ATP-Binding Cassette Transporters; D029968:Escherichia coli Proteins; D010710:Phosphates
keywords: Escherichia coli; phosphate-binding protein; phosphate-binding protein (PBP)