title: Substrate specificity and ionic regulation of GlnPQ from Lactococcus lactis. An ATP-binding cassette transporter with four extracytoplasmic substrate-binding domains.
abstract: We report on the functional characterization of GlnPQ, an ATP-binding cassette transporter with four extracytoplasmic substrate-binding domains. The first predicted transmembrane helix of GlnP was cleaved off in the mature protein and most likely serves as the signal sequence for the extracytoplasmic substrate-binding domains. Deletion analysis showed that the substrate-binding domain, in the primary sequence of GlnP nearest to the translocator domain, is used as the receptor that delivers the substrate to the translocator. Membrane reconstitution of the detergent-solubilized and purified GlnPQ complex yielded proteoliposomes that transported glutamine and glutamic acid at the expense of ATP. The transport activity of GlnPQ increased with lumenal salt concentration and internal pH, but the mechanism of ionic activation of the transporter is distinct from that of other osmoregulatory ATP-binding cassette transporters and does not depend on the presence of anionic lipids. The regulation of GlnPQ conforms to an electrostatic switch in which protein domain(s) and low molecular weight electrolytes participate.
authors.affiliation: Department of Biochemistry, Groningen Biomolecular Science and Biotechnology Institute, University of Groningen, 9747 AG Groningen, The Netherlands.
authors.forename: Gea K
authors.initials: GK
authors.lastname: Schuurman-Wolters
authors.forename: Bert
authors.initials: B
authors.lastname: Poolman
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D003593:Cytoplasm / Q000378:metabolism*; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D013294:Lactococcus lactis / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009994:Osmolar Concentration; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D017931:DNA Primers; D005973:Glutamine; D018698:Glutamic Acid