7XS3

AlXyn26A E243A-X3X4X

Summary for 7XS3

• Entry DOI: 10.2210/pdb7xs3/pdb
• Descriptor: AlXyn26A E243A-X3X4X, beta-D-xylopyranose-(1-3)-beta-D-xylopyranose-(1-4)-beta-D-xylopyranose (3 entities in total)
• Functional Keywords: mlxase, mutant e243a, complex, x3x4x, hydrolase
• Biological source: Algibacter sp. L4_22
• Total number of polymer chains: 2
• Total formula weight: 78666.74

Authors

Zhang, Y.Z.,Chen, X.L.,Zhao, F.,Yu, C.M. (deposition date: 2022-05-12, release date: 2023-05-17, Last modification date: 2023-11-29)

Primary citation

Zhao, F.,Yu, C.M.,Sun, H.N.,Zhao, L.S.,Ding, H.T.,Cao, H.Y.,Chen, Y.,Qin, Q.L.,Zhang, Y.Z.,Li, P.Y.,Chen, X.L.
A novel class of xylanases specifically degrade marine red algal beta 1,3/1,4-mixed-linkage xylan.
J.Biol.Chem., 299:105116-105116, 2023

PubMed Abstract: Xylans are polysaccharides composed of xylose and include β1,4-xylan, β1,3-xylan, and β1,3/1,4-mixed-linkage xylan (MLX). MLX is widely present in marine red algae and constitutes a significant organic carbon in the ocean. Xylanases are hydrolase enzymes that play an important role in xylan degradation. While a variety of β1,4-xylanases and β1,3-xylanases involved in the degradation of β1,4-xylan and β1,3-xylan have been reported, no specific enzyme has yet been identified that degrades MLX. Herein, we report the characterization of a new MLX-specific xylanase from the marine bacterium Polaribacter sp. Q13 which utilizes MLX for growth. The bacterium secretes xylanases to degrade MLX, among which is Xyn26A, an MLX-specific xylanase that shows low sequence similarities (<27%) to β1,3-xylanases in the glycoside hydrolase family 26 (GH26). We show that Xyn26A attacks MLX precisely at β1,4-linkages, following a β1,3-linkage toward the reducing end. We confirm that Xyn26A and its homologs have the same specificity and mode of action on MLX, and thus represent a new xylanase group which we term as MLXases. We further solved the structure of a representative MLXase, AlXyn26A. Structural and biochemical analyses revealed that the specificity of MLXases depends critically on a precisely positioned β1,3-linkage at the -2/-1 subsite. Compared to the GH26 β1,3-xylanases, we found MLXases have evolved a tunnel-shaped cavity that is fine-tuned to specifically recognize and hydrolyze MLX. Overall, this study offers a foremost insight into MLXases, shedding light on the biochemical mechanism of bacterial degradation of MLX.

PubMed: 37524130
DOI: 10.1016/j.jbc.2023.105116

Experimental method

X-RAY DIFFRACTION (1.9 Å)