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• Authors: Mirjam Czjzek and Gurvan Michel
• Responsible Curator: Mirjam Czjzek

Substrate specificities

The two known members of glycoside hydrolase family 82 enzymes cleave the β-1,4 galactosidic bond of the marine algal polysaccharide iota-carrageenan [1] yielding products of the neocarrabiose series.

Kinetics and Mechanism

Family 82 enzymes are inverting enzymes, as first shown by NMR [1] on the iota-carrageenase from Alteromonas fortis.

Catalytic Residues

From structural analysis predicted to be two out of the three candidate amino acids Glu245, Asp247 or Glu310 in the A. fortis iota-carrageenase [2].

Three-dimensional structures

To date, a crystal structure has only been determined for the iota-carrageenase from A. fortis [2]. The crystal structure of a product complex has shed light on the existance of domain movement of domain A that is closed around the oligo-carrageenan in the complexed form and open in the uncomplexed enzyme [3].

Family Firsts

First sequence identification and family creation

iota-carrageenase sequences have been first reported for enzymes from A. fortis and Z. galactanivorans [1].

First sterochemistry determination

GH82 enzymes are inverting as shown by NMR [1].

First general acid residue identification

not determined yet.

First general base residue identification

not determined yet.

First 3-D structure

iota-carrageenase from A. fortis [2]. The structure belongs to the β-helix fold (PDB 1h80 and PDB 1ktw).

References

1. Barbeyron T, Michel G, Potin P, Henrissat B, and Kloareg B. iota-Carrageenases constitute a novel family of glycoside hydrolases, unrelated to that of kappa-carrageenases. J Biol Chem 2000 Nov 10; 275(45) 35499-505. doi:10.1074/jbc.M003404200 pmid:10934194. PubMed HubMed [1]
2. Michel G, Chantalat L, Fanchon E, Henrissat B, Kloareg B, and Dideberg O. The iota-carrageenase of Alteromonas fortis. A beta-helix fold-containing enzyme for the degradation of a highly polyanionic polysaccharide. J Biol Chem 2001 Oct 26; 276(43) 40202-9. doi:10.1074/jbc.M100670200 pmid:11493601. PubMed HubMed [2]
3. Michel G, Helbert W, Kahn R, Dideberg O, and Kloareg B. The structural bases of the processive degradation of iota-carrageenan, a main cell wall polysaccharide of red algae. J Mol Biol 2003 Nov 28; 334(3) 421-33. pmid:14623184. PubMed HubMed [3]