Effects of glycosylation on protein structure, function and dynamics

近年来，蛋白质结构生物学领域取得了显著进展。然而，人类或复杂的蛋白质经过翻译后修饰(如糖基化、磷酸化和甲基化等)。在蛋白质数据库(PDB)中很少找到，因为这些修改不能由原核蛋白表达宿主(如大肠杆菌)充分执行。在翻译后修饰中，蛋白质糖基化是自然界中发现的最丰富的蛋白质修饰，它给蛋白质带来的多样性比所有其他翻译后修饰的总和还要多。蛋白质的糖基化改变了蛋白质的结构、热力学和动力学，从而调节蛋白质的功能，影响蛋白质的定位、转运、溶解性、抗原性、生物活性、半衰期和细胞与细胞的相互作用。因此，在发育和某些疾病中，糖链结构和糖基化模式是高度动态和变化的，这并不令人惊讶。到目前为止，蛋白质糖基化对功能的影响还知之甚少。更重要的是，关于这种翻译后修饰的结构信息很少。事实上，从结构生物学的角度来看，糖基化是不受欢迎的，由于寡糖链的大小、灵活性和异质性，糖基化通常被认为是解决蛋白质结构的额外障碍。在研究单元中，我们的小组(P6 Schwalbe)希望通过核磁共振波谱研究糖基化对糖蛋白结构、功能和动力学的影响。为此，我们将开发特定的核磁共振工具(表达、同位素标记、核磁共振方法)，在第一个资助期对糖基化蛋白质进行研究。在研究单元中，我们将重点介绍三种高度保守的糖基化途径(N-糖基化、C-甘露糖化和O-甘露糖化)，它们基于脂多糖醇，竞争甘露糖供体底物和受体蛋白。在这个研究单位的组装过程中，我们已经开始与(P1 Bakker)合作，通过核磁共振从结构上研究色氨酸C-甘露糖基化的影响。

Recent years have seen remarkable progress in the field of structural biology of proteins. However, human or complex proteins with posttranslational modifications (like glycosylation, phosphorylation and methylation etc.) are rarely found in the Protein Data Bank (PDB), since these modifications cannot be performed sufficiently by prokaryotic protein expression hosts like Escherichia coli. Among the posttranslational modifications, protein glycosylation is the most abundant protein modification found in nature, introducing more diversity into the protein than all the other posttranslational modifications combined. Glycosylation of proteins changes their structure, thermodynamics and kinetics, which modulate the function of the proteins and influence their localization, trafficking, solubility, antigenicity, biological activity, half-life and cell-cell interactions. Therefore, it is not surprising that glycan structures and glycosylation patterns are highly dynamic and change during development and in certain diseases. So far, the effects of protein glycosylation on function are poorly understood. Even more, structural information regarding this posttranslational modification is rare. In fact, from a structural biology perspective glycosylation is undesired and is often considered as an additional obstacle to solve a protein structure due to the size, flexibility and heterogeneity of the oligosaccharide chains. In the Research Unit our group (P6 Schwalbe) wants to study the influence of glycosylation on the structure, function and dynamics of glycoproteins by NMR spectroscopy. For this purpose, we will develop specific NMR tools (expression, isotope labeling, NMR methods) to conduct research on glycosylated proteins in the first funding period. In the Research Unit we will focus on three highly conserved glycosylation pathways (N-glycosylation, C-mannosylation and O-mannosylation) which are based on the lipid dolichol and compete for both mannosyl donor substrates and acceptor proteins. In the course of the assembly of this Research Unit we already started to structurally investigate the effect of tryptophan C-mannosylation by NMR in collaboration with (P1 Bakker).