Dubey Vinod S, Sirakova Tatiana D, Kolattukudy P E
Neurobiotechnology Center, Department of Biochemistry, The Ohio State University, 1060 Carmack Road, Columbus, OH 43210, USA.
Mol Microbiol. 2002 Sep;45(5):1451-9. doi: 10.1046/j.1365-2958.2002.03119.x.
Cell wall lipids of Mycobacterium tuberculosis containing multiple methylbranched fatty acids play critical roles in pathogenesis and thus offer targets for new antimycobacterial drugs. Mycocerosicacid synthase gene (mas) encodes the enzyme that produces one class of such acids. Seven mas-like genes (msls) were identified in the genome. One of them, msl3, originally annotated as two separate genes, pks 3 and pks 4, is now shown to constitute a single open reading frame, which encodes a 220.3 kDa protein. Msl3 was disrupted using a phage mediated delivery system and the gene replacement in the mutant was confirmed by polymerase chain reaction analysis of the flanking regions of the introduced disrupted gene and by Southern analysis. Biochemical analysis showed that the msl3 mutant does not produce mycolipanoic acids and mycolipenic(phthienoic) acids, the major constituents of polyacyl trehaloses and thus lacks this cell wall lipid, but synthesizes all of the other classes of lipids. The absence of the major acyl chains that anchor the surface-exposed acyltrehaloses causes a novel growth morphology; the cells stick to each other, most probably via the intercellular interaction between the exposed hydrophobic cell surfaces, manifesting a bead-like growth morphology without affecting the overall growth rate.
结核分枝杆菌细胞壁中含有多种甲基支链脂肪酸的脂质在发病机制中起关键作用,因此为新型抗分枝杆菌药物提供了靶点。分枝菌酸合酶基因(mas)编码产生一类此类酸的酶。在基因组中鉴定出七个类mas基因(msls)。其中一个基因msl3,最初被注释为两个独立的基因pks 3和pks 4,现在显示它构成一个单一的开放阅读框,编码一种220.3 kDa的蛋白质。使用噬菌体介导的递送系统破坏了msl3,并通过对引入的破坏基因侧翼区域的聚合酶链反应分析和Southern分析证实了突变体中的基因替换。生化分析表明,msl3突变体不产生多酰海藻糖的主要成分——分枝脂酸和分枝脂烯(噻吩烯酸),因此缺乏这种细胞壁脂质,但能合成所有其他类别的脂质。锚定表面暴露的酰基海藻糖的主要酰基链的缺失导致了一种新的生长形态;细胞相互粘附,很可能是通过暴露的疏水细胞表面之间的细胞间相互作用,表现出念珠状生长形态,而不影响总体生长速率。