Characterization of an Unknown Region Linked to the Glycoside Hydrolase Family 17 β-1,3-Glucanase of Vibrio vulnificus Reveals a Novel Glucan-Binding Domain

The glycoside hydrolase family 17 beta-1,3-glucanase of Vibrio vulnificus (VvGH17) has two unknown regions in the N- and C-termini. Here, we characterized these domains by preparing mutant enzymes. VvGH17 demonstrated hydrolytic activity of beta-(1 -> 3)-glucan, mainly producing laminaribiose, but not of beta-(1 -> 3)/beta-(1 -> 4)-glucan. The C-terminal-truncated mutants (Delta C466 and Delta C441) showed decreased activity, approximately one-third of that of the WT, and Delta C415 lost almost all activity. An analysis using affinity gel containing laminarin or barley beta-glucan revealed a shift in the mobility of the Delta C466, Delta C441, and Delta C415 mutants compared to the WT. Tryptophan residues showed a strong affinity for carbohydrates. Three of four point-mutations of the tryptophan in the C-terminus (W472A, W499A, and W542A) showed a reduction in binding ability to laminarin and barley beta-glucan. The C-terminus was predicted to have a beta-sandwich structure, and three tryptophan residues (Trp472, Trp499, and Trp542) constituted a putative substrate-binding cave. Linker and substrate-binding functions were assigned to the C-terminus. The N-terminal-truncated mutants also showed decreased activity. The WT formed a trimer, while the N-terminal truncations formed monomers, indicating that the N-terminus contributed to the multimeric form of VvGH17. The results of this study are useful for understanding the structure and the function of GH17 beta-1,3-glucanases.

Automated summary

In this study, the glycoside hydrolase family 17 beta-1,3-glucanase of Vibrio vulnificus (VvGH17) was characterized by preparing mutant enzymes. The C-terminus was found to be important for the enzyme's activity and substrate-binding ability, while the N-terminus contributed to the multimeric form of VvGH17. These findings provide insights into the structure and function of GH17 beta-1,3-glucanases.