Armbruster Krista M, Meredith Timothy C
Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA.
Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA
J Bacteriol. 2017 May 9;199(11). doi: 10.1128/JB.00099-17. Print 2017 Jun 1.
Bacterial lipoproteins are embedded in the cell membrane of both Gram-positive and Gram-negative bacteria, where they serve numerous functions central to cell envelope physiology. Lipoproteins are tethered to the membrane by an -acyl--(mono/di)-acyl-glyceryl-cysteine anchor that is variously acylated depending on the genus. In several low-GC, Gram-positive firmicutes, a monoacyl-glyceryl-cysteine with an N-terminal fatty acid (known as the lyso form) has been reported, though how it is formed is unknown. Here, through an intergenic complementation rescue assay in , we report the identification of a common orthologous transmembrane protein in both and that is capable of forming lyso-form lipoproteins. When deleted from the native host, lipoproteins remain diacylated with a free N terminus, as maturation to the -acylated lyso form is abolished. Evidence is presented suggesting that the previously unknown gene product functions through a novel intramolecular transacylation mechanism, transferring a fatty acid from the diacylglycerol moiety to the α-amino group of the lipidated cysteine. As such, the discovered gene has been named ipoprotein ntramolecular ransacylase (), to differentiate it from the gene for the intermolecular -acyltransferase () involved in triacyl lipoprotein biosynthesis in Gram-negative organisms. This study identifies a new enzyme, conserved among low-GC, Gram-positive bacteria, that is involved in bacterial lipoprotein biosynthesis and synthesizes lyso-form lipoproteins. Its discovery is an essential first step in determining the physiological role of N-terminal lipoprotein acylation in Gram-positive bacteria and how these modifications impact bacterial cell envelope function.
细菌脂蛋白嵌入革兰氏阳性菌和革兰氏阴性菌的细胞膜中，在那里它们发挥着许多对细胞包膜生理学至关重要的功能。脂蛋白通过一个酰基-（单/二）-酰基甘油-半胱氨酸锚定在膜上，该锚定根据菌属的不同而有不同的酰化形式。在几种低GC含量的革兰氏阳性厚壁菌中，已报道了一种带有N端脂肪酸的单酰甘油-半胱氨酸（称为溶菌形式），但其形成方式尚不清楚。在这里，通过在[具体菌种]中的基因间互补拯救试验，我们报告了在[两种菌种名称]中鉴定出一种共同的直系同源跨膜蛋白，它能够形成溶菌形式的脂蛋白。当从天然宿主中缺失该蛋白时，脂蛋白仍保持二酰化且N端游离，因为向酰化溶菌形式的成熟过程被消除了。有证据表明，这个以前未知的基因产物通过一种新的分子内转酰基机制发挥作用，将脂肪酸从二酰甘油部分转移到脂化半胱氨酸的α-氨基上。因此，这个发现的基因被命名为脂蛋白分子内转酰基酶（ItrA），以区别于参与革兰氏阴性菌三酰脂蛋白生物合成的分子间酰基转移酶（Lgt）基因。这项研究鉴定出一种在低GC含量的革兰氏阳性细菌中保守的新酶，它参与细菌脂蛋白的生物合成并合成溶菌形式的脂蛋白。它的发现是确定革兰氏阳性菌中N端脂蛋白酰化的生理作用以及这些修饰如何影响细菌细胞包膜功能的重要第一步。
