title: Core component EccB1 of the Mycobacterium tuberculosis type VII secretion system is a periplasmic ATPase.
abstract: Pathogenic mycobacteria transport virulence factors across their complex cell wall via a type VII secretion system (T7SS)/early secreted antigenic target-6 of kDa secretion system (ESX). ESX conserved component (Ecc) B, a core component of the T7SS architecture, is predicted to be a membrane bound protein, but little is known about its structure and function. Here, we characterize EccB1, showing that it is an ATPase with no sequence or structural homology to other ATPases located in the cell envelope of Mycobacterium tuberculosis H37Rv. We obtained the crystal structure of an EccB1-ΔN72 truncated transmembrane helix and performed modeling and ATP docking studies, showing that EccB1 likely exists as a hexamer. Sequence alignment and ATPase activity determination of EccB1 homologues indicated the presence of 3 conserved motifs in the N- and C-terminals of EccB1-ΔN72 that assemble together between 2 membrane proximal domains of the EccB1-ΔN72 monomer. Models of the EccB1 hexamer show that 2 of the conserved motifs are involved in ATPase activity and form an ATP binding pocket located on the surface of 2 adjacent molecules. Our results suggest that EccB may act as the energy provider in the transport of T7SS virulence factors and may be involved in the formation of a channel across the mycomembrane.
authors.affiliation: *State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China; National Laboratory of Biomacromolecules and Laboratory of RNA Biology, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China; and Graduate School, Chinese Academy of Sciences, Beijing, China.
authors.forename: Xiao-Li
authors.initials: XL
authors.lastname: Zhang
authors.affiliation: *State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China; National Laboratory of Biomacromolecules and Laboratory of RNA Biology, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China; and Graduate School, Chinese Academy of Sciences, Beijing, China.
authors.forename: De-Feng
authors.initials: DF
authors.lastname: Li
authors.affiliation: *State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China; National Laboratory of Biomacromolecules and Laboratory of RNA Biology, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China; and Graduate School, Chinese Academy of Sciences, Beijing, China.
authors.forename: Joy
authors.initials: J
authors.lastname: Fleming
authors.affiliation: *State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China; National Laboratory of Biomacromolecules and Laboratory of RNA Biology, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China; and Graduate School, Chinese Academy of Sciences, Beijing, China.
authors.forename: Li-Wei
authors.initials: LW
authors.lastname: Wang
authors.affiliation: *State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China; National Laboratory of Biomacromolecules and Laboratory of RNA Biology, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China; and Graduate School, Chinese Academy of Sciences, Beijing, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: *State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China; National Laboratory of Biomacromolecules and Laboratory of RNA Biology, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China; and Graduate School, Chinese Academy of Sciences, Beijing, China zhangxe@sun5.ibp.ac.cn blj@ibp.ac.cn.
authors.forename: Da-Cheng
authors.initials: DC
authors.lastname: Wang
authors.affiliation: *State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China; National Laboratory of Biomacromolecules and Laboratory of RNA Biology, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China; and Graduate School, Chinese Academy of Sciences, Beijing, China zhangxe@sun5.ibp.ac.cn blj@ibp.ac.cn.
authors.forename: Xian-En
authors.initials: XE
authors.lastname: Zhang
authors.affiliation: *State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China; National Laboratory of Biomacromolecules and Laboratory of RNA Biology, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China; and Graduate School, Chinese Academy of Sciences, Beijing, China zhangxe@sun5.ibp.ac.cn blj@ibp.ac.cn.
authors.forename: Li-Jun
authors.initials: LJ
authors.lastname: Bi
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009169:Mycobacterium tuberculosis / Q000201:enzymology / Q000378:metabolism*; D019897:Periplasm / Q000201:enzymology*; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D017301:Ca(2+) Mg(2+)-ATPase
keywords: ESX-1; crystal structure; virulence