The overall structure of XynA
The full-length XynA protein was expressed and purified with removal of nucleic acids by anion exchange column QHP. XynA contains 408 residues and the molecular weight of the tagged full-length protein was 49.8 kDa with an isoelectric point of 6.64. It was identified as one monomer in the solution by gel filtration (Figure 1A) . We found that xylanase 10A (SlXyn10A, PDB code 1V0L) fromS. lividans has the highest sequence similarity (30%) with XynA by using Phyre2 server (Gloster et al., 2004; Kelley, Mezulis, Yates, Wass, & Sternberg, 2015). We used this structure as a search model to solve the crystal structure of XynA by molecular replacement method.
The determined 2.3 Å crystal structure of XynA (residues 22-393) with aR free of 0.245 (Table 1 ). The space group is P4122 , and one molecule was present in the asymmetric unit. In the refined model, residues Leu52, Ala53, Asp359, Ala360, Asn361, Gly378, and Glu379 are missing due to disordered configuration. The XynA structure is composed of 12 α-helices and 14 β-sheets, among which α2-α11 helices and β3-β10 sheets form a classical (α/β)8 TIM-barrel fold(Figure 1B) . Overall, the mug-shaped XynA is comprised of an N-terminal domain (residues 1-67), GH10 domain (residues 68-326) and C-terminal domain (residues 327-408) (Figure 1C) . The body of “mug” is GH10 domain, which has 3 α-helices separated by loop regions, named α2, α4, and α7 (Figure 1B) . These three α-helices are not affecting the overall conformation of classical (α/β)8 TIM-barrel fold.