Harrison James, Lloyd Georgina, Joe Maju, Lowary Todd L, Reynolds Edward, Walters-Morgan Hannah, Bhatt Apoorva, Lovering Andrew, Besra Gurdyal S, Alderwick Luke J
Institute of Microbiology and Infection, School of Biosciences, University of Birmingham, Birmingham, United Kingdom.
Alberta Glycomics Centre and Department of Chemistry, University of Alberta, Gunning-Lemieux Chemistry Centre, Edmonton, Canada.
mBio. 2016 Aug 2;7(4):e00972-16. doi: 10.1128/mBio.00972-16.
Mycobacterium tuberculosis, the etiological agent of tuberculosis (TB), has a unique cell envelope which accounts for its unusual low permeability and contributes to resistance against common antibiotics. The main structural elements of the cell wall consist of a cross-linked network of peptidoglycan (PG) in which some of the muramic acid residues are covalently attached to a complex polysaccharide, arabinogalactan (AG), via a unique α-l-rhamnopyranose-(1→3)-α-d-GlcNAc-(1→P) linker unit. While the molecular genetics associated with PG and AG biosynthetic pathways have been largely delineated, the mechanism by which these two major pathways converge has remained elusive. In Gram-positive organisms, the LytR-CpsA-Psr (LCP) family of proteins are responsible for ligating cell wall teichoic acids to peptidoglycan, through a linker unit that bears a striking resemblance to that found in mycobacterial arabinogalactan. In this study, we have identified Rv3267 as a mycobacterial LCP homolog gene that encodes a phosphotransferase which we have named Lcp1. We demonstrate that lcp1 is an essential gene required for cell viability and show that recombinant Lcp1 is capable of ligating AG to PG in a cell-free radiolabeling assay.
Tuberculosis is an infectious disease caused by the bacterial organism Mycobacterium tuberculosis Survival of M. tuberculosis rests critically on the integrity of its unique cell wall; therefore, a better understanding of how the genes and enzymes involved in cell wall assembly work is fundamental for us to develop new drugs to treat this disease. In this study, we have identified Lcp1 as an essential phosphotransferase that ligates together arabinogalactan and peptidoglycan, two crucial cell wall macromolecules found within the mycobacterial cell wall. The discovery of Lcp1 sheds new light on the final stages of mycobacterial cell wall assembly and represents a key biosynthetic step that could be exploited for new anti-TB drug discovery.
结核分枝杆菌是结核病（TB）的病原体，具有独特的细胞壁，这导致其通透性异常低，并使其对常见抗生素具有抗性。细胞壁的主要结构成分是肽聚糖（PG）的交联网络，其中一些胞壁酸残基通过独特的α-L-鼠李吡喃糖-（1→3）-α-D-葡萄糖胺-（1→P）连接单元与复合多糖阿拉伯半乳聚糖（AG）共价连接。虽然与PG和AG生物合成途径相关的分子遗传学已基本明确，但这两条主要途径如何汇聚的机制仍不清楚。在革兰氏阳性菌中，LytR-CpsA-Psr（LCP）蛋白家族负责通过一个与分枝杆菌阿拉伯半乳聚糖中发现的连接单元惊人相似的连接单元，将细胞壁磷壁酸连接到肽聚糖上。在本研究中，我们鉴定出Rv3267是一种分枝杆菌LCP同源基因，它编码一种磷酸转移酶，我们将其命名为Lcp1。我们证明lcp1是细胞存活所必需的基因，并表明重组Lcp1能够在无细胞放射性标记试验中将AG连接到PG上。
结核病是由细菌病原体结核分枝杆菌引起的传染病。结核分枝杆菌的存活严重依赖于其独特细胞壁的完整性；因此，更好地了解参与细胞壁组装的基因和酶如何发挥作用，对于我们开发治疗这种疾病的新药至关重要。在本研究中，我们鉴定出Lcp1是一种必需的磷酸转移酶，它将阿拉伯半乳聚糖和肽聚糖连接在一起，这是分枝杆菌细胞壁中发现的两种关键的细胞壁大分子。Lcp1的发现为分枝杆菌细胞壁组装的最后阶段提供了新的线索，并代表了一个关键的生物合成步骤，可用于发现新的抗结核药物。
