GALACTOSYLTRANSFERASES--STRUCTURE AND REGULATION

糖基转移酶催化细胞和细胞外分子上特定寡糖结构的合成，这些寡糖结构在正常和病理状态下的生物识别过程中具有关键作用;一些糖基转移酶还充当膜结合碳水化合物受体，另一些糖基转移酶在发育调节中具有重要作用。 然而，关于这些重要酶的结构、相互作用和机制的信息很少。 两个半乳糖基转移酶将被调查，催化反应，其中转移的单糖的构型被保留和反转，分别。 然而，共享的序列基序表明，这些酶的至少一部分可能是远亲。 α-半乳糖基转移酶催化半乳糖基-α-1，3-半乳糖基-β-OR结构的合成;该酶在人体中失活，约1%的内源性抗体针对其作用产物α-gal表位，并代表器官异种移植的主要障碍。 这种酶的机制及其结构基础将通过对可用晶体的动力学、突变和协作X射线衍射分析来研究，这些晶体的分辨率为2.0埃单位。 结果将提供有关催化血型A和B聚糖和Forrssman糖脂合成的同源酶特异性基础的信息。 β-4-半乳糖基转移酶-1是人体内催化β-半乳糖转移至糖蛋白和糖脂中的N-乙酰葡糖胺或葡萄糖的六种同源酶之一。α-乳白蛋白（一种与溶菌酶同源的乳腺特异性蛋白）的结合调节酶的特异性，使其能够在泌乳期间催化乳糖生物合成（半乳糖转化为葡萄糖）。 结构和突变的方法将被用来研究通过这种蛋白质-蛋白质相互作用的调节的基础。 一种新的α-乳白蛋白和溶菌酶的同源物已被鉴定为睾丸表达的cDNA。 这缺乏溶菌酶催化位点，并与α-乳白蛋白有一些相似之处，提高了它可能是一种新的糖基转移酶调节蛋白的可能性。将使用该蛋白的重组形式研究活性和结构。

Glycosyltransferases catalyze the synthesis of specific oligosaccharide structures on cells and extracellular molecules that have crucial roles in biological recognition processes in normal and pathological states; some also act as membrane-bound carbohydrate receptors and others are important in the regulation of development. However, there is little information available on the structures, interactions, and mechanisms of these important enzymes. Two galactosyltransferases will be investigated that catalyze reactions in which the configuration of the transferred monosaccharide is retained and inverted, respectively. However, shared sequence motifs suggest that, at least parts of these enzymes may be distantly related. Alpha- Galactosyltransferase catalyze the synthesis of a galactosyl- alpha-1,3-galactosyl-beta-OR structure; this enzyme is inactivated in humans and about 1 percent of endogenous antibodies are directed against the product of its action, the alpha-gal epitope, and represent a major barrier to the xenotransplantation of organs. The mechanism of this enzyme and its structural basis will be investigated by kinetic, mutational and collaborative X-ray diffraction analysis of available crystals that diffract to 2.0 Angstrom units resolution. The results will provide information about the basis of specificity in homologous enzymes that catalyze the synthesis of blood group A and B glycans and Forrssman glycolipid. Beta-4- Galactosyltransferase-1, is one of six homologous enzymes in humans that catalyze the transfer of beta-galactose to N- acetylglucosamine or glucose in glycoproteins and glycolipids. The binding of alpha-lactalbumin, a mammary specific protein that is homologous with lysozyme, modulates the specificity of the enzyme to allow it to catalyze lactose biosynthesis (galactose transfer to glucose) during lactation. Structural and mutational approaches will be used to investigate the basis of regulation through this protein-protein interaction. A new homologue of alpha-lactalbumin and lysozyme has been identified as a testis- expressed cDNA. This lacks the lysozyme catalytic site and has some similarities to alpha-lactalbumin, raising the possibility that it could be a novel glycosyltransferase regulatory protein. The activity and structure will be investigated using a recombinant form of this protein.