Fig. 6

Cartoon representation of the AlphaFold predicted for XsaEXLX1 structure (www.alphafold.ebi.ac.uk). A six-residue linker region, highlighted in yellow, joins two tightly packed domains, D1 and D2, observed in the solved crystal structures of related plant and microbial expansins. The β-strands and α-helices are colored in blue and red, respectively. The N-terminal D1 domain adopts a double-Y barrel fold (DPBB) and the C-terminal D2 domain adopts a β-sandwich with an Ig-like fold. Three conserved residues in the D1 domain, D100, Y102, and D111 (side chains highlighted as spheres), contribute to expansin function via an unknown mechanism. Three conserved and linearly arranged aromatic residues in the D2 domain, Y154, W155, and Y186 (side chains highlighted as spheres) are expected to promote binding to cellulosic structures. Together these two regions on both domains form one continuous surface on the same face of XsaEXLX1