Improvement of the stability and catalytic efficiency of heparan sulfate N-sulfotransferase for preparing N-sulfated heparosan.

The chemo-enzymatic and enzymatic synthesis of heparan sulfate and heparin are considered as an attractive alternative to the extraction of heparin from animal tissues. Sulfation of the hydroxyl group at the position 2 of the deacetylated glucosamine is a prerequisite for subsequent enzymatic modifications. In this study, multiple strategies including truncation mutagenesis based on B-factor values, site-directed mutagenesis guided by multiple sequence alignment and structural analysis were performed to improve the stability and activity of human N-sulfotransferase. Eventually, a combined variant Mut02 (MBP-hNST-NΔ599-602/S637P/S741P/E839P/L842P/K779N/R782V) was successfully constructed, whose half-life at 37 °C and catalytic activity were increased by 105-fold and 1.35-fold, respectively. After efficient overexpression using the Escherichia coli expression system, the variant Mut02 was applied to N-sulfation of the chemically deacetylated heparosan. The N-sulfation content reached around 82.87% which was nearly 1.88-fold higher than that of the wild-type. The variant Mut02 with high stability and catalytic efficiency has great potential for heparin biomanufacturing.