MUTATIONAL APPROACHES TO INVESTIGATION OF PROTEIN STRUCTURE, FUNCTION & FOLDING

人CDI蛋白是一个非主要组织相容性蛋白家族， 复合物（MHC）编码的跨膜糖蛋白表达， 与抗原呈递表面上的02-微球蛋白的缔合 细胞（APC）。 与众所周知的M[HC] I类和11类不同， 将肽抗原呈递给T细胞的蛋白质，人类I组 CD 1蛋白（CD 1a、CD 1b和CD 1c）介导特异性T细胞识别 细菌脂质和糖脂抗原。 以往的研究 分支杆菌特异性T细胞已经识别出两类 CDI限制性脂质抗原。 这些是游离的分枝菌酸， α-支链的0-羟基长链脂肪酸家族，以及 含磷脂酰肌醇的糖脂，包括 脂阿拉伯甘露聚糖（LAM）和磷脂酰肌醇甘露糖苷（PlMs）。 麻风分枝杆菌感染最近揭示了证据， 第三类CDI限制性脂质抗原。 CDI蛋白质发挥着 在特异性T细胞识别外源脂质中的核心作用 抗原，但脂质抗原的分子机制 介绍是未知的。 在过去的一年里，我们已经确定 一种新的CDI限制性糖脂抗原--葡萄糖单霉菌酸盐 （GM[M]），它允许对结构进行系统分析， 决定其被T细胞识别的特征。 GNM的类似物 它们的酰基链长度和其他 脂质部分的化学特征被T细胞识别。 在 相反，T细胞对碳水化合物表现出良好的特异性， 一份？真菌酰糖脂，甚至区分 碳水化合物异构体的不同之处仅在于一个单一的取向 羟基（例如，只有葡萄糖而没有甘露糖或半乳糖）。 在 结合最近对CD 1晶体结构的研究， 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呈递 非特异性地位于CD 1的深层疏水口袋内， 蛋白质，导致呈现的亲水性元素 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.