MUTATIONAL APPROACHES TO INVESTIGATION OF PROTEIN STRUCTURE, FUNCTION & FOLDING

人CDI蛋白是一个具有正常组织相容性的家族 复合体(MHC)编码的跨膜糖蛋白在 与抗原提呈表面02-微球蛋白的相关性 细胞(APC)。不同于众所周知的M[HC I类和11类 将多肽抗原呈递给T细胞的蛋白质，人类I组 CD1蛋白(CD1a、CD1b和CD1c)介导特异性T细胞识别 细菌脂类和糖脂抗原。以前的研究 分枝杆菌特异性T细胞已鉴定出两类 CDI限制性脂类抗原。这些是游离的霉菌酸，一种 Cc-支链，0-羟基长链脂肪酸家族，以及 含磷脂酰肌醇的糖脂，包括 脂阿拉伯甘露糖(LAM)和磷脂酰肌醇甘露糖苷(PLMS)。 麻风分枝杆菌感染最近发现了一种证据 第三类CDI限制脂类抗原。CDI蛋白扮演着一个 异物脂质特异性T细胞识别的中枢作用 抗原，但脂质抗原背后的分子机制 具体情况尚不清楚。在过去的一年里，我们已经确定了 一种新的CDI限制性糖脂抗原--单乙酸葡萄糖 (GM[M)，这使得能够对结构进行系统分析 决定其被T细胞识别的特征。GNM类似物 在酰基链长和其他方面有很大不同 T细胞识别脂类成分的化学特征。在……里面 相比之下，T细胞对这种碳水化合物表现出很好的特异性 霉菌糖脂的一部分，甚至可以区分 碳水化合物异构体只在单个碳水化合物的取向上不同 羟基(例如，只有葡萄糖，不含甘露糖或半乳糖)。在……里面 结合最近对CD1晶体结构的研究，这些 这些结果为抗原的分子模型提供了强有力的支持 抗原的酰基链相对结合的表现形式 非特异性地位于CD1的深部疏水口袋内 蛋白质，导致亲水性元素的呈现 与T细胞受体高度特异性相互作用的抗原。

Human CDI proteins are a family of norimajor histocompatibility complex (MHC) encoded transmembrane glycoproteins expressed in association with 02-microglobulin on the surface of antigen-presenting cells (APCs). Unlike the well known M[HC class I and class 11 proteins that present peptide antigens to T cells, the human group I CD1 proteins (CD1a, CD1b andCDlc) mediate specific T cell recognition of bacterial lipid and glycolipid antigens. Previous studies of mycobacteria specific T cells have identified two classes of CDI-restricted lipid antigens. These are the free mycolic acids, a family of cc-branched, 0-hydroxy long chain fatty acids, and the phosphatidylinositol-containing glycolipids including lipoarabinomannan (LAM) andthe phosphatidylinositol mannosides (PlMs). Mycohacterium leprae infection has recently revealed evidence for a third class of CDI restricted lipid antigens. The CDI proteins play a central role in the specific T cell recognition of foreign lipid antigens, but the molecular mechanisms underlying lipid antigen presentation are not known. During this past year, we have identified a novel CDI-restricted glycolipid antigen, glucose monomycolate (GM[M), which is allowing a systematic analysis of the structural features that determine its recognition by T cells. Analogues of GNM that differed substantially in their acyl chain lengths and other chemical features of the lipid moiety were recognized by T cells. In contrast, T cells demonstrated fine specificity for the carbohydrate portion ?of mycolyl glycolipids, even discriminating among carbohydrate isomers differing only in the orientation of a single hydroxyl group (e.g., only glucose and not mannose or galactose). In combination with recent studies of the crystal structure of CD1, these results provide strong support for a molecular model of antigen presentation in which the acyl chains of the antigen bind relatively nonspecifically within the deep, hydrophobic pocket of the CD1 protein, resulting in presentation of the hydrophilic elements of antigens for highly specific interactions with the T cell receptor.