Structural analyses of Legionella LepB reveal a new GAP fold that catalytically mimics eukaryotic RasGAP

• Published in: Cell research Vol. 23; no. 6; pp. 775 - 787
• Main Authors: Yu, Qin, Hu, Liyan, Yao, Qing, Zhu, Yongqun, Dong, Na, Wang, Da-Cheng, Shao, Feng
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.06.2013; Nature Publishing Group
• Subjects: 631/45/173; 631/535; 631/80/313; 631/80/313/2011; Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacterial Proteins - ultrastructure; Biomedical and Life Sciences; Catalytic Domain; Cell Biology; Crystallography, X-Ray; Escherichia coli Proteins - metabolism; GAP; GTPase; GTPase-Activating Proteins - metabolism; Legionella pneumophila; Legionella pneumophila - metabolism; Life Sciences; Mutation; Original; original-article; Pathogens; Protein Folding; Protein Structure, Tertiary; rab1 GTP-Binding Proteins - metabolism; Residues; 催化活性; 军团菌; 模仿; 真核; 结构分析; 谷氨酰胺; TBC GAP; type IV secretion system; GTPase-activating protein (GAP); Rab GTPases; membrane trafficking
• DOI: 10.1038/cr.2013.54
• ISSN: 1001-0602; 1748-7838

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 Legionellapneumophila. We map LepB GAP domain to residues 313-618 and show that the GAP domain is Rabl 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 Rabl-GDP-AIF3 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 Rabl binding, which induces Rabl Gin70 side-chain flipping towards GDP-AIF3 through a strong ionic interaction. This conformationally rearranged Gin70 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.