Structural insights into the regulation of pneumococcal peptidoglycan homeostasis

• 作 者: Qiong Li Wang Cheng Xiao-Hui Bai Hui-Jie Chen Juan Zhang Yi-Hu Yang Yong-Liang Jiang Yuxing Chen Cong-Zhao Zhou
• 机 构: Hefei National Laboratory for Physical Sciences at the Microscale and School of Life Sciences,Univer
• 出 处: 中国生物化学与分子生物学会2016年全国学术会议
• 发表日期: 2016年3期
• 关键词: Streptococcus pneumoniae peptidoglycan homeostasis LytA LytB DacB

　　Peptidoglycan(PG),the main and specific component of bacterial cell wall,is essential for bacterial survival,and its homeostasis is related to cell growth and division.The homeostasis of PG involves not only synthesis controlled by a group of PG synthases,but also remodeling regulated by a series of hydrolases.However,structures and biochemical mechanisms of most hydrolases from Streptococcus pneumoniae,and how they are involved in PG homeostasis remains unknown.We solved the full-length structure of the major autolysin LytA from S.pneumoniae at 2.1 (A) resolution,which cleaves the lactyl-amide bond that links the stem peptides and the glycan strands of the PG.Through site-directed mutageneses combined with enzymatic activity assays,we suggest that dimerization and full occupancy of all choline-binding sites through binding to choline-containing TA chains enable LytA to adopt the fully active conformation,which allows the amidase domain to cleave two lactyl-amide bonds located about 103 (A) Apart on the PG.We report the 1.65 (A) Crystal structure of the catalytic domain of pneumococcal endo-β-N-acetylglucosaminidase LytB(LytBCAT),which cleaves the β(1,4)-glycosidic bond between NAG and NAM.All three modules of LytBCAT,SH3b,WW and GH73,are necessary for its optimal activity towards PG hydrolysis and for pneumococcal adhesion to respiratory epithelial cells.We solved the 1.71 (A) Resolution crystal structure of S.pneumoniae DacB,which sequentially cleave the last two alanine residues of the PG short peptides together with DacA.It adopts a zinc-dependent carboxypeptidase fold and belongs to the metallopeptidase M15B subfamily.Enzymatic activity assays further confirm that DacB indeed acts as an L,D-carboxypeptidase towards the PG stem.