Controlling carrageenan structure using a novel formylglycine-dependent sulfatase, an endo-4S-iota-carrageenan sulfatase.

Carrageenans are sulfated polysaccharides that are found in the cell walls of red algae. These polysaccharides have gelling and texturizing properties that are widely appreciated in industrial applications. However, these functional properties depend strongly on the sulfation of the moieties of the carrabiose repetition unit. Here we aimed to monitor the sulfate composition of gelling carrageenan. To do so, we screened and purified from Pseudoalteromonas atlantica a 4S-iota carrageenan sulfatase that converts ι-carrabiose into α-carrabiose units. The sequence of this protein matched the annotated Q15XH3 (Uniprot databank) formylglycine-dependent sulfatase found in the P. atlantica genome. With pure enzyme, ι-carrageenan could be transformed into a hybrid ι-/α-carrageenan or pure α-carrageenan. Analysis of the distribution of the carrabiose moieties in hybrid carrageenan chain using enzymatic degradation with Alteromonas fortis ι-carrageenase, coupled with chromatography and NMR spectroscopy experiments, showed that the sulfatase has an endo mode of action. The endo-character and the specificity of the sulfatase made it possible to prepare hybrid κ-/ι-/α-carrageenan and κ-/α-carrageenan starting from κ-/ι-carrageenan.