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The currently characterized glycoside hydrolases of this family are endo-acting α-fucosidases active on sulfated fucans (or fucoidans) from brown algae. All described GH107 family members are endo-1,4-fucanase of bacterial origin, and together with enzymes from the CAZY family GH29, they form the clan GH-R. Sequences of GH107 family members were first reported in 2006 [1], even though the enzymatic activity was reported earlier.
Kinetics and Mechanism
Figure 1: Mechanism of family GH107, according to [2].
The mechanism was demonstrated to be consistent with a classical Koshland double-displacement mechanism mechanism by observation of the formation of an α-O-linked mercaptoethanol on a L-Fuc-2,3-disulfate-(α1-3)-L-Fuc-2-sulfate disaccharide by transglycosylation [2]. The same mechanism is demonstrated by GH29 members, consistent with their common membership in Clan GH-R.
The catalytic nucleophile is an aspartate, while the catalytic acid-base is a histidine (Figures 2 and 3). The later is unusual in GHs, and a divergence from GH29, but is likely necessary to avoid electronic repulsion with the substrate sulfate groups. These two residues have been identified by structural superimposition with GH29 enzymes, and are conserved within the few members of the GH107 family. The catalytic His has been further confirmed by the lack of activity of the H294Q mutant of Mariniflexile fucanivorans [2]. The catalytic aspartate was also proposed to be one of the catalytic residue on sequence analysis alone, in a simultaneously released paper [3].
Three-dimensional structures
The crystal structures of Mariniflexile fucanivorans (PDB: 6dns, 6dms, 6dlh) and Psychromonas sp. (PDB: 6m8n) have been determined in 2018 [2]. The Psychromonas sp. (PDB: 6m8n) enzyme showed a single catalytic domain with a (β/α)8 / TIM-barrel fold (Figure 2), while in the Mariniflexile fucanivorans enzyme, this catalytic domain is followed by three Ig-like domains that wrap around the catalytic one [2].
Family Firsts
First stereochemistry determination
The retaining mechanism was determined in 2018 [2].
First catalytic nucleophile identification
An aspartic acid side chain acting as a catalytic nucleophile was identified by two simultaneous studies in the Autumn of 2018 [2, 3].
First general acid/base residue identification
A histidine sidechain acting as a catalytic acid-base residue was identified in 2018 [2].
First 3-D structure
The crystal structures of Mariniflexile fucanivorans (PDB: 6dns,6dms,6dlh) and Psychromonas sp. (PDB: 6m8n) have been released at the same time, in 2018 [2].
