title: Structural analyses of Legionella LepB reveal a new GAP fold that catalytically mimics eukaryotic RasGAP.
abstract: Rab GTPases are emerging targets of diverse bacterial pathogens. Here, we perform biochemical and structural analyses of LepB, a Rab GTPase-activating protein (GAP) effector from Legionella pneumophila. We map LepB GAP domain to residues 313-618 and show that the GAP domain is Rab1 specific with a catalytic activity higher than the canonical eukaryotic TBC GAP and the newly identified VirA/EspG family of bacterial RabGAP effectors. Exhaustive mutation analyses identify Arg444 as the arginine finger, but no catalytically essential glutamine residues. Crystal structures of LepB313-618 alone and the GAP domain of Legionella drancourtii LepB in complex with Rab1-GDP-AlF3 support the catalytic role of Arg444, and also further reveal a 3D architecture and a GTPase-binding mode distinct from all known GAPs. Glu449, structurally equivalent to TBC RabGAP glutamine finger in apo-LepB, undergoes a drastic movement upon Rab1 binding, which induces Rab1 Gln70 side-chain flipping towards GDP-AlF3 through a strong ionic interaction. This conformationally rearranged Gln70 acts as the catalytic cis-glutamine, therefore uncovering an unexpected RasGAP-like catalytic mechanism for LepB. Our studies highlight an extraordinary structural and catalytic diversity of RabGAPs, particularly those from bacterial pathogens.
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Qin
authors.initials: Q
authors.lastname: Yu
authors.forename: Liyan
authors.initials: L
authors.lastname: Hu
authors.forename: Qing
authors.initials: Q
authors.lastname: Yao
authors.forename: Yongqun
authors.initials: Y
authors.lastname: Zhu
authors.forename: Na
authors.initials: N
authors.lastname: Dong
authors.forename: Da-Cheng
authors.initials: DC
authors.lastname: Wang
authors.forename: Feng
authors.initials: F
authors.lastname: Shao
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure*; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D029968:Escherichia coli Proteins / Q000378:metabolism; D020690:GTPase-Activating Proteins / Q000378:metabolism*; D016952:Legionella pneumophila / Q000378:metabolism; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D020761:rab1 GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C429282:EspG protein, E coli; D020690:GTPase-Activating Proteins; C482639:LepB protein, Legionella pneumophila; D020761:rab1 GTP-Binding Proteins