Establishment of an efficient structure-based protein clustering strategy to discovery the galactose...

Sulfation at the 4-OH position of galactose or its derivatives is a common and significant modification for polysaccharides. It confers different biological activities to polysaccharides and can be obtained by sulfonate group transfer, which is catalyzed by galactose 4-O-sulfotransferase (G4ST). Consequently, G4STs serves as a valuable tool for investigating the impact of sulfation on biological activity and for the synthesis of novel sulfated sugars. Despite its significance, only a few vertebrate-derived G4STs have been characterized, highlighting the need for exploring G4STs from diverse sources and for understanding of their structure-function relationships. In this study, we attempted for the first time to identify G4STs derived from microbes. Amino acid sequence screening was conducted, followed by protein structure prediction and clustering, resulting in 100 candidate proteins, which were classified into four clades. Notably, we successfully confirmed G4ST activity in one protein from clade1, named BST61. Structural insight into BST61 revealed the key residues involved in substrate binding, and, more importantly, a three residues-surrounded and conserved spatial position functioning in galactose recognition was determined. Using the conserved spatial position as a robust filter to re-screen the 100 candidate proteins, new sulfotransferases towards galactose were discovered as expected. These findings provided precise methods for mining G4STs, greatly expanding the application of G4STs for the analysis and preparation of sulfated sugars.