# Characterization of BrGH3A, a bovine rumen-derived glycoside hydrolase family 3 β-glucosidase with a permuted domain arrangement

## TL;DR

A new β-glucosidase enzyme, BrGH3A, was identified from bovine rumen microbes and found to have a unique structure and function.

## Contribution

Discovery of BrGH3A, a novel β-glucosidase with a permuted domain arrangement from bovine rumen metagenome.

## Key findings

- BrGH3A is a 92-kDa β-glucosidase with a unique domain arrangement.
- It shows higher catalytic efficiency for laminaribiose than cellobiose.
- It may degrade β-1,3-/1,4-mixed linkage glucans in grass cell walls.

## Abstract

The bovine rumen contains a large consortium of residential microbes that release a variety of digestive enzymes for feed degradation. However, the utilization of these microbial enzymes is still limited because these rumen microorganisms are mostly anaerobes and are thus unculturable. Therefore, we applied a sequence-based metagenomic approach to identify a novel 2,445-bp glycoside hydrolase family 3 β-glucosidase gene known as BrGH3A from the metagenome of bovine ruminal fluid. BrGH3A β-glucosidase is a 92-kDa polypeptide composed of 814 amino acid residues. Unlike most glycoside hydrolases in the same family, BrGH3A exhibited a permuted domain arrangement consisting of an (α/β)6 sandwich domain, a fibronectin type III domain and a (β/α)8 barrel domain. BrGH3A exhibited greater catalytic efficiency toward laminaribiose than cellobiose. We proposed that BrGH3A is an exo-acting β-glucosidase from Spirochaetales bacteria that is possibly involved in the intracellular degradation of β-1,3-/1,4-mixed linkage glucans that are present in grass cell walls. BrGH3A exhibits rich diversity in rumen hydrolytic enzymes and may represent a member of a new clan with a permuted domain topology within the large family.