Detected hexosylated Mmc proteins.

Protein glycosylation has been reported in all forms of life. The genus Mycoplasma is composed of highly genome-streamlined bacterial symbionts, making them model organisms for investigating minimal genome concepts. Previous work from our group showed mycoplasmas scavenge hexoses from exogenous oligosaccharides to glycosylate surface proteins at serine, threonine, asparagine, and glutamine residues without utilizing a consensus sequence as seen in canonical glycosylation systems. We report here that this surface protein hexosylation system is conserved in Mycoplasma genitalium, a human urogenital pathogen with a 580-kbp genome that can be cultured axenically. We also report this modification is found in the ruminant pathogen Mycoplasma mycoides subsp. capri and is conserved in JCVI-Syn3A, a nonpathogenic mycoplasma with a synthetic minimal M. mycoides genome containing genes that are essential for survival and robust growth under axenic culture conditions. In contrast to known glycoproteins, we have detected evidence of glycosylation of aspartic acid and glutamic acid residues, which expands the pool of potential glycosyl acceptors in bacteria to include the acidic amino acids.蛋白质糖基化现象已在所有生命类群中被证实存在。支原体属（Mycoplasma）是一类基因组高度精简的细菌共生体，因此成为研究最小基因组概念的模式生物。本团队此前的研究表明，支原体可从外源寡糖中摄取己糖，在丝氨酸、苏氨酸、天冬酰胺和谷氨酰胺残基上对表面蛋白进行糖基化修饰，且无需像经典糖基化系统那样使用共有序列。本研究证实，该表面蛋白己糖糖基化系统在生殖支原体（Mycoplasma genitalium）中保守存在——这是一种可纯培养的人类泌尿生殖道病原体，其基因组大小为580千碱基对（kbp）。本研究同时发现，该修饰在反刍动物病原体丝状支原体山羊亚种（Mycoplasma mycoides subsp. capri）中存在，并在JCVI-Syn3A中保守存在；JCVI-Syn3A是一株非致病性支原体，其基因组为合成的最小丝状支原体基因组，包含纯培养条件下生存与旺盛生长所必需的基因。与已知糖蛋白不同，本研究检测到天冬氨酸与谷氨酸残基发生糖基化的证据，这将细菌中潜在的糖基化受体残基拓展至酸性氨基酸范畴。