title: The V-motifs facilitate the substrate capturing step of the PTS elevator mechanism.
abstract: We propose that the alternative crystal forms of outward open UlaA (which are experimental, not simulated, and contain the substrate in the cavity) can be used to interpret/validate the MD results from MalT (the substrate capture step, which involves the mobile second TMSs of the V-motifs, TMSs 2 and 7). Since the crystal contacts are the same between the two alternative crystal forms of outward open UlaA, the striking biological differences noted, including rearranged hydrogen bonds and salt bridge coordination, are not attributable to crystal packing differences. Using transport assays, we identified G58 and G286 as essential for normal vitamin C transport, but the comparison of alternative crystal forms revealed that these residues to unhinge TMS movements from substrate-binding side chains, rendering the mid-TMS regions of homologous TMSs 2 and 7 relatively immobile. While the TMS that is involved in substrate binding in MalT is part of the homologous bundle that holds the two separate halves of the transport assembly (two proteins) together, an unequal effect of the two knockouts was observed for UlaA where both V-motifs are free from such dimer interface interactions.
authors.affiliation: Department of Molecular Biology, University of California at San Diego, La Jolla, CA 92093-0116, USA. Electronic address: msaier@ucsd.edu.
authors.forename: Ake
authors.initials: A
authors.lastname: Vastermark
authors.affiliation: Department of Molecular Biology, University of California at San Diego, La Jolla, CA 92093-0116, USA.
authors.forename: Adelle
authors.initials: A
authors.lastname: Driker
authors.affiliation: Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry and Institute of Biomedical Sciences, Fudan University, Shanghai, People's Republic of China.
authors.forename: Jingwei
authors.initials: J
authors.lastname: Weng
authors.affiliation: Laboratory of Cell Biology, Howard Hughes Medical Institute, The Rockefeller University, New York, NY 10065, USA.
authors.forename: Xiaochun
authors.initials: X
authors.lastname: Li
authors.affiliation: State Key Laboratory of Biomembrane and Membrane Biotechnology, School of Life Sciences, Tsinghua University, Beijing, People's Republic of China.
authors.forename: Jiawei
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Molecular Biology, University of California at San Diego, La Jolla, CA 92093-0116, USA.
authors.forename: Milton H
authors.initials: MH
authors.lastname: Saier
mesh_terms: D001205:Ascorbic Acid / Q000737:chemistry; D018360:Crystallography, X-Ray; D019281:Dimerization; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000648:ultrastructure; D006860:Hydrogen Bonding; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000648:ultrastructure; D008958:Models, Molecular; D011487:Protein Conformation; D013379:Substrate Specificity
chemical_list: D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; C473320:SgaT protein, E coli; D001205:Ascorbic Acid