Unusual Enzymes in Carbohydrate Biosynthesis

Newswise — Scientists at Iowa State University have advanced glycomics — the system-wide study of carbohydrates — with the discovery of previously unknown enzymes that synthesize activated sugars.

The proteins, produced from genes found in deep sea archaea that grow at the temperature of boiling water, make key building blocks involved in carbohydrate metabolism, the researchers found. In addition, the Iowa State team has co-opted these heat-stable enzymes to substantially simplify the synthesis of unnatural versions of the building blocks.

The research is the first study in archaea of a class of key enzymes that biosynthesize carbohydrates. Archaea, bacteria and eukaryotes (plants and humans) are the three major branches of life, based on similarities in biochemistry and organization.

The research, "Unusually Broad Substrate Tolerance of a Heat-Stable Archaeal Sugar Nucleotidyltransferase for the Synthesis of Sugar Nucleotides," was published in the Dec. 15 print edition of The Journal of the American Chemical Society. A related article, "One-Step Synthesis of Labeled Sugar Nucleotides for Protein O-GlcNAc Modification Studies by Chemical Function Analysis of an Archaeal Protein," is in press at the same journal.

The research team is led by Nicola Pohl, assistant professor of chemistry and a researcher in the Plant Sciences Institute at Iowa State. Others are postdoctoral researcher Rahman Mizanur and graduate students Corbin Zea and Firoz Jaipuri.

The researchers produced two archaeal proteins and discovered through biochemical studies that they were much better at making a range of sugar biosynthesis intermediates than the enzymes from yeast (a eukaryote) and Escherichia coli (the common lab bacteria). In addition, the researchers determined that both enzymes are much more heat stable than comparable proteins and should be easier to store and use.

"Archaea appears to be a great place to go prospecting for useful biocatalysts," Pohl said.

"Now we can use just one protein instead of needing many to make natural and nonnatural intermediates necessary to study the enzymes called glycosyltransferases that attach sugars to a range of compounds such as lipids, other sugars and proteins," Pohl said.

The researchers produced a second archaeal protein that can make in one step what comparable chemical syntheses did in eight or more steps, Pohl said. The resulting compound is a nonnatural intermediate useful to identify human and plant proteins modified by the single sugar N-acetylglucosamine as part of signaling pathways. Signaling pathways allow cells to respond to outside signals such as stress or specific chemicals.

"Despite their enormous functional and structural diversity, our understanding of carbohydrates is still in its infancy," she said.