title: Nucleotide-free MalK drives the transition of the maltose transporter to the inward-facing conformation.
abstract: The complex MalFGK2 hydrolyzes ATP and alternates between inward- and outward-facing conformations during maltose transport. It has been shown that ATP promotes closure of MalK2 and opening of MalFG toward the periplasm. Yet, why the transporter rests in a conformation facing the cytosol in the absence of nucleotide and how it returns to this state after hydrolysis of ATP is unknown. The membrane domain MalFG may be naturally stable in the inward-facing conformation, or the ABC domain may catalyze the transition. We address this question by analyzing the conformation of MalFG in nanodiscs and in proteoliposomes. We find that MalFG alone exists in an intermediate state until MalK binds and converts the membrane domain to the inward-facing state. We also find that MalK, if overly-bound to MalFG, blocks the transition of the transporter, whereas suppressor mutations that weaken this association restore transport. MalK therefore exploits hydrolysis of ATP to reverse the conformation of MalFG to the inward-facing conformation, a step essential for release of maltose in the cytosol.
authors: From the Department of Biochemistry and Molecular Biology, Life Sciences Institute, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia V6T1Z3, Canada.
authors: Huan
authors: H
authors: Bao
authors: Franck
authors: F
authors: Duong
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000235:genetics / Q000378:metabolism; D001693:Biological Transport, Active / Q000502:physiology; D002384:Catalysis; D003600:Cytosol / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D019897:Periplasm / Q000235:genetics / Q000378:metabolism; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary
chemical_list: D018528:ATP-Binding Cassette Transporters; D029968:Escherichia coli Proteins; C461639:MalF protein, E coli; C079123:MalG protein, E coli; C489398:MalK protein, E coli; D009004:Monosaccharide Transport Proteins; D000255:Adenosine Triphosphate
keywords: ABC Transporter; ATPase; Lipids; Membrane Proteins; Nanodiscs; Protein Complexes; Transport