Fathy Mohamed Yasmine, Hamad Mohamad, Ortega Ximena P, Valvano Miguel A
Centre for Experimental Medicine, School of Medicine, Dentistry and Biomedical Sciences, Queen's University Belfast, Belfast, BT9 7BL, UK.
Department of Microbiology and Immunology, Faculty of Pharmacy, Alexandria University, Alexandria, Egypt.
Mol Microbiol. 2017 Apr;104(1):144-162. doi: 10.1111/mmi.13618. Epub 2017 Jan 27.
Lipid A anchors the lipopolysaccharide (LPS) to the outer membrane and is usually composed of a hexa-acylated diglucosamine backbone. Burkholderia cenocepacia, an opportunistic pathogen, produces a mixture of tetra- and penta-acylated lipid A. "Late" acyltransferases add secondary acyl chains to lipid A after the incorporation of four primary acyl chains to the diglucosamine backbone. Here, we report that B. cenocepacia has only one late acyltransferase, LpxL (BCAL0508), which adds a myristoyl chain to the 2' position of lipid A resulting in penta-acylated lipid A. We also identified PagL (BCAL0788), which acts as an outer membrane lipase by removing the primary β-hydroxymyristate (3-OH-C14:0) chain at the 3 position, leading to tetra-acylated lipid A. Unlike PagL, LpxL depletion caused reduced cell growth and defects in cell morphology, both of which were suppressed by overexpressing the LPS flippase MsbA (BCAL2408), suggesting that lipid A molecules lacking the fifth acyl chain contributed by LpxL are not good substrates for the flippase. We also show that intracellular B. cenocepacia within macrophages produced more penta-acylated lipid A, suggesting lipid A penta-acylation in B. cenocepacia is required not only for bacterial growth and morphology but also for adaptation to intracellular lifestyle.
脂多糖（LPS）通过脂质A锚定在外膜上，脂质A通常由一个六酰化二葡糖胺主链组成。洋葱伯克霍尔德菌是一种机会致病菌，可产生四酰化和五酰化脂质A的混合物。“晚期”酰基转移酶在四条初级酰基链掺入二葡糖胺主链后，将二级酰基链添加到脂质A上。在此，我们报道洋葱伯克霍尔德菌只有一种晚期酰基转移酶LpxL（BCAL0508），它将一条肉豆蔻酰链添加到脂质A的2'位，从而产生五酰化脂质A。我们还鉴定出PagL（BCAL0788），它作为一种外膜脂肪酶，通过去除3位的初级β-羟基肉豆蔻酸（3-OH-C14:0）链，产生四酰化脂质A。与PagL不同，LpxL缺失导致细胞生长减少和细胞形态缺陷，而过表达LPS翻转酶MsbA（BCAL2408）可抑制这两种情况，这表明缺乏LpxL贡献的第五条酰基链的脂质A分子不是翻转酶的良好底物。我们还表明，巨噬细胞内的洋葱伯克霍尔德菌产生更多的五酰化脂质A，这表明洋葱伯克霍尔德菌中的脂质A五酰化不仅对细菌生长和形态是必需的，而且对适应细胞内生活方式也是必需的。
