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

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.