title: The cyclization of the 3,6-anhydro-galactose ring of iota-carrageenan is catalyzed by two D-galactose-2,6-sulfurylases in the red alga Chondrus crispus.
abstract: Carrageenans are sulfated galactans found in the cell walls of numerous red seaweeds (Rhodophyta). They are classified according to the number and the position of sulfate ester groups and the occurrence of 3,6-anhydro-galactose. Although the carrageenan biosynthesis pathway is not fully understood, it is usually accepted that the last step consists of the formation of a 3,6-anhydro ring found in kappa- and iota-carrageenans through the enzymatic conversion of d-galactose-6-sulfate or d-galactose-2,6-disulfate occurring in mu- and nu-carrageenan, respectively. We purified two enzymes, sulfurylase I (65 kD) and sulfurylase II (32 kD), that are able to catalyze the conversion of nu- into iota-carrageenan. We compared their sulfate release rates (i.e. arising from the formation of the anhydro ring) with the viscosity of the solution and demonstrated two distinct modes of action. In addition, we found that some mixtures of sulfurylase I and II lead to the formation of carrageenan solutions with unexpectedly low viscosities. We discuss the implication of these findings for the assembly of a densely aggregated matrix in red algal cell walls.
authors.affiliation: Marine Plants and Biomolecules (UMR7139), Pierre and Marie Curie University-CNRS, Station Biologique, F-29682 Roscoff cedex, France.
authors.forename: Sabine
authors.initials: S
authors.lastname: Genicot-Joncour
authors.forename: Alexandra
authors.initials: A
authors.lastname: Poinas
authors.forename: Odile
authors.initials: O
authors.lastname: Richard
authors.forename: Philippe
authors.initials: P
authors.lastname: Potin
authors.forename: Brian
authors.initials: B
authors.lastname: Rudolph
authors.forename: Bernard
authors.initials: B
authors.lastname: Kloareg
authors.forename: William
authors.initials: W
authors.lastname: Helbert
mesh_terms: D020418:Algal Proteins / Q000302:isolation & purification / Q000378:metabolism*; D019883:Alkyl and Aryl Transferases / Q000302:isolation & purification / Q000378:metabolism*; D002351:Carrageenan / Q000378:metabolism*; D044723:Chondrus / Q000201:enzymology*; D005690:Galactose / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D020418:Algal Proteins; C117625:3,6-anhydrogalactose; D002351:Carrageenan; D019883:Alkyl and Aryl Transferases; D005690:Galactose