Copyright: © Bio VI Figure: ASTB was reengineered by KnowVolution toward a versatile tool for sulfation of sugar and glycosaminoglycans.

Glycosaminoglycans are mostly sulfated polysaccharides playing significant roles in signal transduction, anti-coagulation, detoxification, and many more. Full chemical synthesis of glycosaminoglycans is still a very hard task due to many synthesis steps that affect the final yields. A suitable and sustainable alternative is represented by the in vitro synthesis of sulfated polysaccharides such as cellulose or chitin that mimic functionalities of glycosaminoglycans. Enzymatic sulfation of polysaccharide building blocks by sulfotransferases is synthetically attractive due to their ability to perform highly chemoselective sulfation in aqueous solution and at ambient temperature. The bacterial aryl sulfotransferase B - ASTB was reengineered to improve the sulfation activity toward the cellulose building block, cellobiose. A full KnowVolution campaign was performed. After screening 3,067 ASTB variants, Leu446 and Val579 were identified as beneficial positions to show positive effects on the ASTB activity.

Advancement of an aryl sulfotransferase toward a synthetically attractive sulfation agent for saccharides

Computational studies suggested that Leu446Pro conveys more flexibility to the substrate-binding site and Val579Lys is a distal substitution. Finally, the recombination of Leu446Pro and Val579Lys yielded a variant ASTB-M5 with up to 7.6-fold increased specific activity of ASTB toward cellobiose. A monosulfation of cellobiose was confirmed via mass spectrometry indicating a very selective sulfation. Furthermore, conversion was increased from 33.8% to 87.1% by the ASTB variant in the synthesis of the monosulfated glycosaminoglycan-building block, N-acetylglucosamine. Structure elucidation confirmed a partially regioselective monosulfation at C-3 and C-4 position, opposed to the chemically preferred C-6.

This work was a successful collaboration between Professor Schwaneberg and Professor Elling from RWTH Aachen and Professor Křen from Czech Academy of Sciences. Our work was financed by the projects FuPol, BioSulfa and the German Federal Ministry of Education and Research. For more detail, access this publication in our Research Highlights and Chemistry – A European Journal website.