The first crystal structure of a family 31 carbohydrate‐binding module with affinity to β‐1,3‐xylan

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Abstract
Here, we present the crystal structure of the family 31 carbohydrate‐binding module (CBM) of β‐1,3‐xylanase from Alcaligenes sp. strain XY‐234 (AlcCBM31) determined at a resolution of 1.25 Å. The AlcCBM31 shows affinity with only β‐1,3‐xylan. The AlcCBM31 molecule makes a β‐sandwich structure composed of eight β‐strands with a typical immunoglobulin fold and contains two intra‐molecular disulfide bonds. The folding topology of AlcCBM31 differs from that of the large majority of other CBMs, in which eight β‐strands comprise a β‐sandwich structure with a typical jelly‐roll fold. AlcCBM31 shows structural similarity with CBM structures of family 34 and family 9, which also adopt structures based on immunoglobulin folds.