MYCOKETIDES: NOVEL M TUBERCULOSIS PKS12 PRODUCT PRESENTED BY CD1C TO T CELLS

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。对cd1c介导的T细胞反应的脂质靶点的研究最近发现了一种分枝杆菌磷脂抗原，其碳水化合物结构与哺乳动物甘露糖基b-1-磷脂醇（MPD）精确对应，但含有不寻常的脂质部分。在这里，我们发现这种T细胞抗原是一个分支链烷烃脂类家族的成员，其长度不同（C30-34），由结核分枝杆菌、牛分枝杆菌-卡尔梅特- guerin和其他生长在细胞内的分枝杆菌产生。对这些分枝杆菌抗原精细结构的分析表明，区分它们与哺乳动物MPDs的化学特征是激活cd1c限制性T细胞所必需的，但不能用任何已知的脂质生物合成途径来解释。代谢标记和质谱分析表明，脂质以C5增量延长的机制是严格交替结合C2和C3单元，而不是焦磷酸异戊烯酯缩合。对结核分枝杆菌基因组的检查发现了一个基因pks12，该基因预计会产生蛋白质组中最大的蛋白质，并包含12个催化结构域，这是进行这种多步骤合成所必需的。基因缺失和互补表明PKS12对于抗原产生和cd1c介导的T细胞活化是必要和充分的，但不影响真正异戊二醇的合成。这些研究建立了一种以前未知的分枝杆菌聚酮的遗传和酶基础，被称为分枝杆菌酮，它代表了一种脂质病原体相关的分子模式，允许分枝杆菌被人类免疫系统识别。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Study of the lipid targets of CD1c-mediated T cell responses recently identified a mycobacterial phospholipid antigen whose carbohydrate structure precisely corresponded to mammalian mannosyl b-1-phosphodolichols (MPD), but contained an unusual lipid moiety. Here we show that this T cell antigen is a member of a family of branched, alkane lipids that vary in length (C30-34) and are produced by M. tuberculosis, M. bovis Bacille-Calmette-Guerin and other mycobacteria that grow within cells. Analysis of the fine structures of these mycobacterial antigens showed that the chemical features that distinguished them from mammalian MPDs were necessary for activation of CD1c-restricted T cells, but could not be accounted for by any known lipid biosynthetic pathway. Metabolic labeling and mass spectrometric analyses suggested a mechanism for elongating lipids in C5 increments by strictly alternating incorporation of C2 and C3 units, rather than isopentenyl pyrophosphate condensation. Inspection of the M. tuberculosis genome identified one gene pks12, which is predicted to make the largest protein in the proteome and to contain 12 catalytic domains necessary to carry out this multi-step synthesis. Genetic deletion and complementation showed that PKS12 was necessary and sufficient for antigen production and the resulting CD1c-mediated T cell activation, but did not affect synthesis of true isoprenols. These studies establish the genetic and enzymatic basis for a previously unknown type of mycobacterial polyketide, designated mycoketide, which represents a lipidic pathogen associated molecular pattern that allows mycobacterial recognition by the human immune system.