Uncovering an enzyme’s unexpected activity

The enzyme sulfatase has been found to be able to catalyse a reaction it was presumed to be incapable of¹, expanding our understanding of biologically critical biomolecules. The discovery, reported in the Russian Journal of Bioorganic Chemistry, is a great example of how experiments can sometimes lead to serendipitous breakthroughs.

“Our experiment has resulted in new fundamental insights,” says Kirill Bobrov from the research team, which is based at the Laboratory of Enzymology at the Petersburg Nuclear Physics Institute, National Research Center Kurchatov Institute, in Gatchina, Russia.

Bobrov and his colleagues were seeking an enzyme to cleave chemical sulfate groups, composed of sulfur and oxygen, from large carbohydrate molecules called complex polysaccharides. The team hoped that sulfatase would catalyse the required hydrolysis reaction, involving the addition of a water molecule, and so break the sulfate bond. Instead, sulfatase was observed to catalyse the hydrolysis of a different molecule that it was not expected to.

The road to the new insight into sulfatase activity began when, puzzled by the lack of the reaction they were expecting, the researchers went back to scour the literature. This led to the discovery that to achieve the activity they were pursuing, the enzyme would need to first undergo a specific chemical modification. In fact, this modification should have been required for any hydrolysis reaction, and so it was all the more surprising that they observed sulfatase activity at all without that modification, even though it was on a different molecule.

“A lesson from this is to be sure to study the literature carefully before starting experiments,” says Bobrov, wryly, “but the unexpected hydrolysis activity we did find interested us.”

This led the team to explore the structure of the enzyme in atomic-level detail. Enzymes are proteins composed of a chain of small molecules called amino acids. Once the protein chain is formed, it folds up in a precise configuration that brings specific amino acid components together to form the catalytic ‘active site’ of the enzyme. By studying the effect of replacing some amino acids with others, the researchers were able to determine the catalytic significance of specific amino acids and, most notably, that an amino acid called cysteine was crucial for the unexpected hydrolysis activity.

The research has revealed key details of how this activity can be achieved without the chemical modification of an amino acid that was previously assumed to be required, opening up a new avenue of research into unmodified sulfatase activity and potential applications.