Chemical synthesis uncovers the significant impact of natural glycosylation on islet amyloid polypeptide aggregation.

Protein and peptide aggregation poses substantial challenges in disease pathology and therapeutic development. While natural glycosylation may mitigate aggregation, its efficacy and underlying mechanisms remain poorly understood due to limited access to homogeneous samples with complex glycans. This study addresses these knowledge gaps by investigating the natural glycosylation of islet amyloid polypeptide (IAPP), a peptide with therapeutic potential for type 2 diabetes but problematic aggregation. An optimized chemical synthesis enabled preparation of diverse IAPP glycoforms with complex glycan structures, allowing systematic evaluation of their effects on aggregation, cytotoxicity, and solubility. Sialylated glycans at Thr completely inhibited IAPP aggregation, eliminated cytotoxicity toward pancreatic β cells, and enhanced solubility by up to 280-fold. Replica exchange molecular dynamics simulations revealed that glycosylation impedes adoption of a four-stranded β-sheet conformation in IAPP dimers. These findings advance the understanding of the role of natural glycosylation in aggregation and highlight its potential as an evolutionarily inspired strategy to enhance the therapeutic utility of IAPP.