title: Maltose-binding protein effectively stabilizes the partially closed conformation of the ATP-binding cassette transporter MalFGK2.
abstract: Maltose transporter MalFGK2is a type-I importer in the ATP-binding cassette (ABC) transporter superfamily. Upon the binding of its periplasmic binding protein, MalE, the ATPase activity of MalFGK2can be greatly enhanced. Crystal structures of the MalFGK2-MalE-maltose complex in a so-called "pretranslocation" ("pre-T") state with a partially closed conformation suggest that the formation of this MalE-stabilized intermediate state is a key step leading to the outward-facing catalytic state. On the contrary, crosslinking and fluorescence studies suggest that ATP binding alone is sufficient to promote the outward-facing catalytic state, thereby doubting the role of MalE binding. To clarify the role of MalE binding and to gain deeper understanding of the molecular mechanisms of MalFGK2, we calculated the free energy surfaces (FESs) related to the lateral motion in the presence and absence of MalE using atomistic metadynamics simulations. The results showed that, in the absence of MalE, laterally closing motion was energetically forbidden but, upon MalE binding, more closed conformations similar to the pre-T state become more stable. The significant effect of MalE binding on the free energy landscapes was in agreement with crystallographic studies and confirmed the important role of MalE in stabilizing the pre-T state. Our simulations also revealed that the allosteric effect of MalE stimulation originates from the MalE-binding-promoted vertical motion between MalF and MalG cores, which was further supported by MD simulation of the MalE-independent mutant MalF500.
authors.affiliation: Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry, and Institutes of Biomedical Sciences, Fudan University, Shanghai, P. R. China. wnwang@fudan.edu.cn.
authors.forename: Jingwei
authors.initials: J
authors.lastname: Weng
authors.affiliation: Department of Chemistry, Institute for Advance Study and School of Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China. xuhuihuang@ust.hk.
authors.forename: Shuo
authors.identifier: http://orcid.org/0000-0002-5895-6924
authors.initials: S
authors.lastname: Gu
authors.affiliation: Computer, Electrical and Mathematical Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia.
authors.forename: Xin
authors.initials: X
authors.lastname: Gao
authors.affiliation: Department of Chemistry, Institute for Advance Study and School of Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China. xuhuihuang@ust.hk.
authors.forename: Xuhui
authors.initials: X
authors.lastname: Huang
authors.affiliation: Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry, and Institutes of Biomedical Sciences, Fudan University, Shanghai, P. R. China. wnwang@fudan.edu.cn.
authors.forename: Wenning
authors.identifier: http://orcid.org/0000-0002-8712-0536
authors.initials: W
authors.lastname: Wang
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000378:metabolism; D003460:Crystallization; D004926:Escherichia coli / Q000737:chemistry* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D058619:Maltose-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D033902:Periplasmic Binding Proteins / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary
chemical_list: D018528:ATP-Binding Cassette Transporters; D029968:Escherichia coli Proteins; C461619:MalE protein, E coli; D058619:Maltose-Binding Proteins; D033902:Periplasmic Binding Proteins; C461599:maltose transport system, E coli