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Members of GH151 are bacterial enzymes presenting α-L-fucosidase activity (EC 3.2.1.51) [1, 2, 3]. Activity has been observed on 4-nitrophenyl-α-L-fucopyranoside (pNP-α-L-Fuc) [2, 3] and on 2-chloro-4-nitrophenyl-α-L-fucopyranoside (CNP-α-L-Fuc) [1]. GH151 α-L-fucosidases are reportedly unable to catalyze hydrolysis of human milk oligosaccharide structures 2'-fucosyllactose (2'FL) and 3-fucosyllactose (3FL) [1, 3], but slight activity has been observed on the blood group H antigen disaccharide Fuc-α-1,2-Gal [1]. No activity was observed on fucosylated xyloglucan [3].
The first characterized members of GH151 were perceived as members of GH29 due to their α-L-fucosidase activity [1, 3]. However, phylogenetic analysis and sequence alignment revealed poor homology to GH29 [1, 3]. Based on the low sequence similarity to GH29, it was suggested that a new GH family be created [2]. Sequence homology to GH42 β-galactosidase trimerization domains has been reported [1, 3]. Consequently, one GH151 α-L-fucosidase was tested for activity on pNP-β-D-Gal, pNP-β-D-Glc, and pNP-β-D-Lac, but none was observed [3].
Kinetics and Mechanism
The catalytic mechanism of GH151 has not been determined, but based on reports that two members of GH151 can catalyze transglycosylation using pNP-α-L-Fuc or CNP-α-L-Fuc as donor substrate [2, 3, 4], a retaining mechanism has been inferred.
Catalytic Residues
In the α-L-fucosidase isoenzyme 2 from Paenibacillus thiaminolyticus, Glu235 was assigned as catalytic acid/base and Asp154 as catalytic nucleophile following a combination of mutational, structural, docking, and QM/MM studies [5]. Initially, both Asp9 and Asp154 were investigated as putative nucleophiles. However, docking studies combined with the fact that the variant D9N performed well in transglycosylation [4] indicated that the role of Asp9 is in substrate binding [5].
Three-dimensional structures
The first solved structure in GH151 was that of α-L-fucosidase isoenzyme 2 from Paenibacillus thiaminolyticus. It revealed a tetrameric structure with active site complementation by His503 [5].
Family Firsts
First stereochemistry determination
Not yet identified.
First catalytic nucleophile identification
Asp154 in α-L-fucosidase isoenzyme 2 from Paenibacillus thiaminolyticus [5].
First general acid/base residue identification
Glu235 in α-L-fucosidase isoenzyme 2 from Paenibacillus thiaminolyticus [5].
First 3-D structure
The 3-D structure of α-L-fucosidase isoenzyme 2 from Paenibacillus thiaminolyticus [5].
