Strategies to Improve Crystallizability of Glycosylated Enzyme

Glycosylation is an important post-translational modification, which has important effects on expression regulation, folding, secretion and function of the proteins. Glycosylated modification mainly exists in eukaryotes, however it is found that some prokaryotes also possess that modification. Depending on the type of amino acid linked to the sugar chain , glycosylation can be divided into N-glycosylation and O-glycosylation. Enzymes are highly specific and efficient biocatalysts produced by living cells , which are proteins or RNA in chemical nature. The role of glycosylation in the internal structure and external function of enzymes has been a research hotspot in recent years , especially the influence on biocatalytic performance and stability. It has attracted much attention due to its far-reaching significance on the design and modification of enzymes. To understand the mechanism of influence made by glycosylation modification on enzyme structure and biocatalytic activity can provide ideas and directions for rational/semi-rational design and modification of enzyme molecules. X-ray crystallography is one of the main methods to study the structures of glycosylated enzymes , which combine X-ray diffraction and protein crystallography. However , complex sugar chains cause chemical and structural heterogeneity of glycosylated enzymes , which hinders crystal formation and crystal diffraction. Hydrolysis treatment with glycosidase , introduction of glycosyltransferase inhibitors and optimization of heterologous expression system are all important strategies to improve the crystallizability of glycosylated enzymes. These methods can improve the homogeneity of glycosylated enzymes while avoiding the damage to stability and catalytic activity of those.