Glycoside Hydrolase Family 82

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

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Glycoside Hydrolase Family GH82
Clan	none
Mechanism	inverting
Active site residues	known
CAZy DB link
http://www.cazy.org/fam/GH82.html

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 the catalytic residues have been predicted to be two out of the three candidate amino acids Glu245, Asp247 or Glu310 in the A. fortis iota-carrageenase [2]. A study in 2010, which utilized site directed mutagenesis, has confirmed that Glu245 plays the role of the general acid residue in this inverting enzyme, while Asp247 is the general base activating the nucleophilic water molecule [3]. However, intriguingly the position of equivalent residues to Asp247 in other iota-carrageenase sequences are not strictly conserved [3, 4].

Three-dimensional structures

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 [5].

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

Glu245 [3].

First general base residue identification

Asp247 [3].

First 3-D structure

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

References

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