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Paenibacillus campinasensis BL11 isolated from black liquor secretes multiple glycoside hydrolases (GHs) against all kinds of polysaccharides. GH consists of a catalytic module and non-catalytic carbohydrate-binding modules (CBMs), in which CBMs append to the catalytic module, mediating specific interactions with insoluble carbohydrates to promote the hydrolysis efficiency of the cognate enzyme. Endo-β-1,4-xylanase (XylX) is one of the GHs reveals high enzymatic activity in a wide range of pH and thermal endurance, suitable for bioconversion and bio-refinement applications. In this work, we report the resonance assignments of a family 36 CBM (characterized as CBM36) derived from XylX. Our investigations will facilitate molecular structure determination and molecular dynamics analysis of CBMs.

Endo‐β‐1, 4‐xylanase (XylX), consisting of catalytic module and non‐catalytic module, was isolated from Paenibacillus campinasensis BL21 from black liquor. XylX displays a great potential for xylan‐degrading applications in biotechnological processing with a wide range of pH and thermal endurance. The catalytic module serves to degrade polysaccharide molecules into small molecules whereas the non‐catalytic module has a sequence similarity to CBM family 36 (denote as PcCBM36) that promotes the association of the enzyme with the carbohydrate substrates. To uncover the structural and functional relationship, we applied various techniques to PcCBM36, including solution NMR, ITC, and CD spectroscopy. The molecular structure of PcCBM36 has been determined by solution NMR. As revealed by the chemical shifts perturbation, we demonstrated that Glu10, Glu12, Asn29 and Asp119 are involved in one of the Ca+2 binding sites and Tyr34, Asp110, Trp114, and Asp115 involved the other, associated with the carbohydrate interaction. Here we demonstrate that binding of PcCBM36 to its substrate, xylohexaose, is Ca+2‐dependent, consistent with previous observations. And the biological roles with respect to these two Ca+2 binding sites and the underlying specific binding mechanism of PcCBM36/xylohexaose are to be elucidated.