title: Structure of pneumococcal peptidoglycan hydrolase LytB reveals insights into the bacterial cell wall remodeling and pathogenesis.
abstract: Streptococcus pneumoniae causes a series of devastating infections in humans. Previous studies have shown that the endo-β-N-acetylglucosaminidase LytB is critical for pneumococcal cell division and nasal colonization, but the biochemical mechanism of LytB action remains unknown. Here we report the 1.65 Å crystal structure of the catalytic domain (residues Lys-375-Asp-658) of LytB (termed LytBCAT), excluding the choline binding domain. LytBCAT consists of three structurally independent modules: SH3b, WW, and GH73. These modules form a "T-shaped" pocket that accommodates a putative tetrasaccharide-pentapeptide substrate of peptidoglycan. Structural comparison and simulation revealed that the GH73 module of LytB harbors the active site, including the catalytic residue Glu-564. In vitro assays of hydrolytic activity indicated that LytB prefers the peptidoglycan from the lytB-deficient pneumococci, suggesting the existence of a specific substrate of LytB in the immature peptidoglycan. Combined with in vitro cell-dispersing and in vivo cell separation assays, we demonstrated that all three modules are necessary for the optimal activity of LytB. Further functional analysis showed that the full catalytic activity of LytB is required for pneumococcal adhesion to and invasion into human lung epithelial cells. Structure-based alignment indicated that the unique modular organization of LytB is highly conserved in its orthologs from Streptococcus mitis group and Gemella species. These findings provided structural insights into the pneumococcal cell wall remodeling and novel hints for the rational design of therapeutic agents against pneumococcal growth and thereby the related diseases.
authors.affiliation: From the Hefei National Laboratory for Physical Sciences at the Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230027, China and.
authors.forename: Xiao-Hui
authors.initials: XH
authors.lastname: Bai
authors.affiliation: From the Hefei National Laboratory for Physical Sciences at the Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230027, China and.
authors.forename: Hui-Jie
authors.initials: HJ
authors.lastname: Chen
authors.affiliation: From the Hefei National Laboratory for Physical Sciences at the Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230027, China and.
authors.forename: Yong-Liang
authors.initials: YL
authors.lastname: Jiang
authors.affiliation: Center for Infectious Disease Research, School of Medicine, Tsinghua University, Beijing 100084, China.
authors.forename: Zhensong
authors.initials: Z
authors.lastname: Wen
authors.affiliation: From the Hefei National Laboratory for Physical Sciences at the Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230027, China and.
authors.forename: Yubin
authors.initials: Y
authors.lastname: Huang
authors.affiliation: From the Hefei National Laboratory for Physical Sciences at the Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230027, China and.
authors.forename: Wang
authors.initials: W
authors.lastname: Cheng
authors.affiliation: From the Hefei National Laboratory for Physical Sciences at the Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230027, China and.
authors.forename: Qiong
authors.initials: Q
authors.lastname: Li
authors.affiliation: From the Hefei National Laboratory for Physical Sciences at the Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230027, China and.
authors.forename: Lei
authors.initials: L
authors.lastname: Qi
authors.affiliation: Center for Infectious Disease Research, School of Medicine, Tsinghua University, Beijing 100084, China zhanglab@tsinghua.edu.cn.
authors.forename: Jing-Ren
authors.initials: JR
authors.lastname: Zhang
authors.affiliation: From the Hefei National Laboratory for Physical Sciences at the Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230027, China and cyxing@ustc.edu.cn.
authors.forename: Yuxing
authors.initials: Y
authors.lastname: Chen
authors.affiliation: From the Hefei National Laboratory for Physical Sciences at the Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230027, China and zcz@ustc.edu.cn.
authors.forename: Cong-Zhao
authors.initials: CZ
authors.lastname: Zhou
mesh_terms: D001422:Bacterial Adhesion; D001483:Base Sequence; D002473:Cell Wall / Q000378:metabolism*; D017931:DNA Primers; D008168:Lung / Q000382:microbiology; D016297:Mutagenesis, Site-Directed; D009238:N-Acetylmuramoyl-L-alanine Amidase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D013296:Streptococcus pneumoniae / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity
chemical_list: D017931:DNA Primers; C119964:LytB protein, Streptococcus; D009238:N-Acetylmuramoyl-L-alanine Amidase
keywords: Bacterial Pathogenesis; Cell Wall Remodeling; Enzyme Structure; Peptidoglycan; Streptococcus; Structural Biology