Syntheses of homogeneous proteoglycan like glycopeptide and glycoprotein libraries for microarray studies

Proteoglycans (PGs) play important roles in many biological processes including inflammatory responses, cancer development, immune modulation, and Alzheimer’s disease. PGs are comprised of heparan sulfate or chondroitin sulfate glycosaminoglycan chains covalently attached to the core protein through tetrasaccharide linkers. Traditionally, the biological functions of PGs are believed to be dominated by the glycosaminoglycan chains attached. However, it has become increasingly appreciated that the core protein can significantly impact glycan activities. Both the core protein and the GAG chains should be considered to fully understand the PG functions. To expedite high throughput screening of the binding between PGs and their partners, the first microarray of PG like glycopeptides/glycoproteins bearing homogeneous glycan structures is proposed for this project. Due to the heterogeneity of glycan sequences in naturally existing PGs, it is extremely challenging to purify well-defined structures to study the structure and activity relationship. Traditional synthetic methods are tedious, which can require over 80 chemical steps to complete a glycopeptide with a glycosaminoglycan chain, severely limiting the synthetic output. Thus, chemical, chemoenzymatic, and chemoselective ligation strategies will be developed to break through the synthetic bottleneck and produce PG like glycopeptides/glycoproteins. These new structures will be incorporated into a PG microarray. The binding between multiple proteins including growth factors, cell adhesion molecules, amyloid β, and Tau with the PG microarray will be screened to better understand the key structure features including the location of GAG chain on the core protein, the number of GAG chain, and the sulfation patterns of GAG on PG for binding. The binding will be further validated in protein and cellular studies. The PG microarray can be a powerful new tool to advance our understanding of the fascinating biological properties of PGs.