Kaixuan Zhou
Xiaolin Yang
Bing Zhang
Yao Zhao
Yu Xiao
Xiuna Yang
Haitao Yang
Luke W. Guddat
Jun Li
Zihe Rao
1 Shanghai Institute for Advanced Immunochemical Studies and School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China;
2 CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, Shanghai 200031, China;
3 State Key Laboratory of Medicinal Chemical Biology, College of Life Sciences and College of Pharmacy, Nankai University, Tianjin 300353, China;
4 Laboratory of Structural Biology, Tsinghua University, Beijing 100084, China;
5 National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China;
6 School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia;
7 University of Chinese Academy of Sciences, Beijing 100101, China
Funds: We are extremely grateful to the National Centre for Protein Science Shanghai (Protein Expression and Purification System) for their instrumental support and technical assistance. We thank the staff from beamlines BL18U and BL19U1 at Shanghai Synchrotron Radiation Facility (Shanghai, China) and beamline BL41XU at SPring-8 (Hyogo, Japan) for assistance during data collection. We also thank Prof. Rongguang Zhang and Dr. Jinwei Zhu for providing laboratory resources. This work was supported by Grants from the National Key Research and Development Program of China (Grant No. 2017YFC0840300), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB08020200), and the National Natural Science Foundation of China (Grant Nos. 81520108019, 31500607).
Received Date: 2019-04-10
Rev Recd Date:2019-07-02
Publish Date:2020-02-10
Abstract
Abstract
Type VII secretion systems (T7SSs) are found in many disease related bacteria including Mycobacterium tuberculosis (Mtb). ESX-1[early secreted antigen 6 kilodaltons (ESAT-6) system 1] is one of the five subtypes (ESX-1～5) of T7SSs in Mtb, where it delivers virulence factors into host macrophages during infection. However, little is known about the molecular details as to how this occurs. Here, we provide high-resolution crystal structures of the C-terminal ATPase3 domains of EccC subunits from four different Mtb T7SS subtypes. These structures adopt a classic RecA-like α/β fold with a conserved Mg-ATP binding site. The structure of EccCb1 in complex with the C-terminal peptide of EsxB identifies the location of substrate recognition site and shows how the specific signaling module "LxxxMxF" for Mtb ESX-1 binds to this site resulting in a translation of the bulge loop. A comparison of all the ATPase3 structures shows there are significant differences in the shape and composition of the signal recognition pockets across the family, suggesting that distinct signaling sequences of substrates are required to be specifically recognized by different T7SSs. A hexameric model of the EccC-ATPase3 is proposed and shows the recognition pocket is located near the central substrate translocation channel. The diameter of the channel is ~25-?, with a size that would allow helix-bundle shaped substrate proteins to bind and pass through. Thus, our work provides new molecular insights into substrate recognition for Mtb T7SS subtypes and also a possible transportation mechanism for substrate and/or virulence factor secretion.Keywords: type VII secretion system,
Mycobacterium tuberculosis,
ATPase,
virulence factor,
substrate recognition
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