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

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 最近对CD1c介导的T细胞反应的脂质靶点的研究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醇b-1-磷酸二醇(MPD)完全一致，但含有不寻常的脂质部分。在这里，我们证明这种T细胞抗原是长度不同的分支烷烃脂(C30-34)家族的成员，由结核分枝杆菌、牛分枝杆菌卡氏杆菌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的精细结构分析表明，它们与哺乳动物MPD不同的化学特征是激活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，通过严格交替结合C2和C3单元，而不是异戊烯基焦磷酸缩合，以C5为增量延长脂质的机制。对结核分枝杆菌基因组的检查发现了一个基因pks12，它被预测为蛋白质组中最大的蛋白质，并包含进行这一多步骤合成所必需的12个催化域。基因缺失和互补表明，PKS12是抗原产生和CD1c介导的T细胞活化的必要条件和充分条件，但不影响真异丙二烯的合成。这些研究为一种以前未知的分枝杆菌聚酮的遗传和酶基础奠定了基础，称为霉酮，它代表了一种脂类病原体相关的分子模式，允许人类免疫系统识别分枝杆菌。

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.