Laboratory of Biochemistry, Institut Químic de Sarrià, Universitat Ramon Llull, Barcelona, Spain.
Sci Rep. 2019 May 8;9(1):7085. doi: 10.1038/s41598-019-42970-9.
Because of the lack of cell wall, Micoplasma species require a fine control of membrane fluidity and integrity. mg517 is an essential gene of Mycoplasma genitalium responsible for the biosynthesis of membrane glycoglycerolipids. It encodes for a unique glycosyltransferase (MG517) with processive activity, transferring activated glycosyl donors to either nude diacylglycerol or already glycosylated diacylglycerol. This dual activity, asserted to different enzymes in other species, is sensitive to and regulated by the presence of anionic lipid vesicles in vitro. We present here a computational model of the C-terminus domain of MG517 that complements a previous structural model of the N-terminus domain. By means of sequence analysis, molecular dynamics and metadynamics simulations, we have identified a short α-helix at the apical C-terminus of MG517 with clear amphipathic character. Binding to a membrane model is thermodynamically favored which suggests that this structural element guides the adhesion of MG517 to the cell membrane. We have experimentally verified that truncation of part of this helix causes a substantial reduction of glycoglycerolipids synthesis. The model proposes that MG517 recognizes and binds the diacylglycerol substrate embedded in the membrane by means of this α-helix at the C-terminus together with a previously identified binding pocket at the N-terminus.
由于缺乏细胞壁，支原体物种需要精细控制膜的流动性和完整性。mg517 是生殖支原体负责膜糖脂生物合成的必需基因。它编码具有连续活性的独特糖基转移酶（MG517），将激活的糖供体转移到裸露的二酰基甘油或已经糖基化的二酰基甘油上。这种双重活性在其他物种中被认为是不同酶的活性，对外源阴离子脂质体在体外的存在敏感且受其调节。我们在这里提出了 MG517 的 C 端结构域的计算模型，该模型补充了以前的 N 端结构域模型。通过序列分析、分子动力学和元动力学模拟，我们在 MG517 的顶端 C 端识别出一个具有明显两亲性的短α-螺旋。与膜模型的结合在热力学上是有利的，这表明这个结构元素指导 MG517 与细胞膜的粘附。我们已经通过实验验证了该螺旋的一部分缺失会导致糖脂合成的大量减少。该模型提出，MG517 通过 C 端的这个α-螺旋以及先前鉴定的 N 端结合口袋来识别和结合嵌入在膜中的二酰基甘油底物。
