Enzymatic activities of proteins encoded by PmurB, PmurC, and PmurE involved in methanogen pseudomurein biosynthesis

Guihong Cha^1*Zhenli Lai²Shuxin Wang²Qing Yang²Pengyan Zhao²Yi Chen²Wei Han³Liping Bai⁴

• ¹School of Food and Liquor Engineering (School of Wuliangye Baijiu), Sichuan University of Science & En-gineering, Yibin, 644005, China., Yibin, China
• ²Biogas Institute of Ministry of Agriculture, Chengdu, China
• ³Jiangsu University, Zhenjiang, China
• ⁴China West Normal University, Nanchong, China

Pseudomurein, a glycan polymer present in the cell wall, is found in the orders Methanobacteriales and Methanopyrales. It possesses glycan units and peptide chains similar to those of bacterial peptidoglycan (murein). However, the biosynthesis of pseudomurein remains unknown. In this study, we identified and characterised several key enzymes, such as PMurBCE ligases, that are proposed to catalyse peptide chain biosynthesis. Specifically, PMurB catalyses the conjugation of UDP-Glu and Pi, forming UDP. PMurC then transfers alanine or threonine to UDP-Glu, and PMurE adds lysine to the PMurC product. These reactions represent the enzymatic activities of PMurBCE ligases in methanogens. Structural model analyses indicated that archaeal PMur enzymes share an overall structural arrangement similar to that of bacterial Mur ligases but exhibit specificity for different substrates. The structural model data provide insights into pseudomurein synthesis in methanogens and create promising avenues for biotechnological applications in methanogens, such as gene editing and the development of novel antibacterial agents targeting methanogenic archaea.