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

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.