exosulfatases

Exosulfatases are enzymes that catalyze the removal of sulfate groups from the terminal, or exocentric, position of their substrates. They represent a subset of sulfatases whose defining feature is exo- rather than endo-action: exosulfatases act on the outermost sulfate ester, whereas endosulfatases remove sulfates from internal positions within a molecule or polymer.

Biochemical properties and mechanism. Many exosulfatases are part of the broader formylglycine-dependent sulfatase family, which relies on a post-translational modification to generate an active formylglycine residue in the catalytic site. The canonical sulfatase signature motif is typically described as a conserved cysteine or serine residue within a C-X-P-S/T-X-R context, which is converted to formylglycine during maturation. Exosulfatases hydrolyze sulfate esters by adding water, yielding a free alcohol and free sulfate.

Distribution and substrates. Exosulfatases have been identified in bacteria, archaea, and eukaryotes, with notable roles in the degradation of sulfated polysaccharides. In marine microbiology, exosulfatases enable bacteria to desulfate and subsequently depolymerize complex algal and seaweed-derived carbohydrates such as carrageenan, fucoidan, and ulvan. They can also act on smaller substrates, including simple aryl sulfate esters, highlighting functional diversity within the class.

Physiological and applied relevance. By removing terminal sulfate groups, exosulfatases facilitate further enzymatic processing and nutrient extraction from sulfated substrates. This activity contributes to sulfur and carbon cycling in the environment and has potential applications in biotechnology, including controlled desulfation in analytical workflows and industrial valorization of sulfated polymers.

See also: sulfatase family, formylglycine-dependent sulfatases, glycosaminoglycan degradation.