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Published January 2012 | public
Journal Article

Inward facing conformations of the MetNI methionine ABC transporter: Implications for the mechanism of transinhibition

Abstract

Two new crystal structures of the Escherichia coli high affinity methionine uptake ATP Binding Cassette (ABC) transporter MetNI, purified in the detergents cyclohexyl-pentyl-β-D-maltoside (CY5) and n-decyl-β-D-maltopyranoside (DM), have been solved in inward facing conformations to resolutions of 2.9 and 4.0 Å, respectively. Compared to the previously reported 3.7 Å resolution structure of MetNI purified in n-dodecyl-β-D-maltopyranoside (DDM), the higher resolution of the CY5 data enabled significant improvements to the structural model in several regions, including corrections to the sequence registry, and identification of ADP in the nucleotide binding site. CY5 crystals soaked with selenomethionine established details of the methionine binding site in the C2 regulatory domain of the ABC subunit, including the displacement of the side chain of MetN residue methionine 301 by the exogenous ligand. When compared to the CY5 or DDM structures, the DM structure exhibits a significant repositioning of the dimeric C2 domains, including an unexpected register shift in the intermolecular β-sheet hydrogen bonding between monomers, and a narrowing of the nucleotide binding space. The immediate proximity of the exogenous methionine binding site to the conformationally variable dimeric interface provides an indication of how methionine binding to the regulatory domains might mediate the phenomenon of transinhibition.

Additional Information

© 2011 The Protein Society. Received 24 September 2011; Revised 6 November 2011; Accepted 7 November 2011. Published online 16 November 2011. Additional Supporting Information may be found in the online version of this article. Grant sponsor: NIH; Grant number: GM045162. A Vietnam International Education Development scholarship to P.T.N. from the Vietnam Ministry of Education and Training scholarship is gratefully acknowledged. The authors thank the Gordon and Betty Moore Foundation and the Sanofi-Aventis Bioengineering Research Program at Caltech for their generous support of the Molecular Observatory at Caltech. Portions of this research were carried out at the Stanford Synchrotron Radiation Lightsource (SSRL), a Directorate of SLAC National Accelerator Laboratory and an Office of Science User Facility operated for the U.S. Department of Energy Office of Science by Stanford University. The SSRL Structural Molecular Biology Program is supported by the DOE Office of Biological and Environmental Research, and by the National Institutes of Health, National Center for Research Resources, Biomedical Technology Program (P41RR001209), and the National Institute of General Medical Sciences. Coordinates and structure factors have been deposited in the Protein Data Bank of the Research Collaboratory for Structural Bioinformatics, with IDs 3TUI, 3TUJ, and 3TUZ for the CY5, DM, and CY5 SeMet soak structures, respectively.

Additional details

Created:
August 22, 2023
Modified:
October 24, 2023