Structural analyses of Legionella LepB reveal a new GAP fold that catalytically mimics eukaryotic RasGAP |
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Authors: | Qin Yu Liyan Hu Qing Yao Yongqun Zhu Na Dong Da-Cheng Wang Feng Shao |
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Affiliation: | 1.National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China;2.National Institute of Biological Sciences, #7 Science Park Rd, Zhongguancun Life Science Park, Beijing 102206, China;3.Life Sciences Institute, Zhejiang University, Hangzhou, Zhejiang 310058, China;4.Graduate University of Chinese Academy of Sciences, Beijing 100049, China |
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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. |
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Keywords: | Legionella Rab GTPases GTPase-activating protein (GAP) type IV secretion system TBC GAP membrane trafficking |
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