Hot spot residues at the protein–protein interface between XBP and XynA by MD simulations. Changes in binding free energy (ΔΔG
bind) on alanine mutation of interface residues for a 2091A and c 2621B. Amino acids with a ΔΔG
bind > 1.0 kcal/mol (red dashed line) are considered to be critical at the interface. b Three hot spot residues (T261, W396 and L402) in the 2091A chimera. T261 and W396 are inserted into a surface cleft of the XBP, and T261 is involved in hydrogen bond formation with a XBP peptide bond (yellow dashed line). d Four hot spot residues (N249, E253, N318 and N407) of the 2621B chimera. The XynA N407 residue has a large contact area with the XBP, participating in four hydrogen bonds (yellow, dashed lines). The interfacial residues are shown as stick representation in yellow, and the XynA moiety as a ribbon. The XBP is shown as a cartoon and solid surface (in gray) and the linker region is in pink. The structures representations were prepared using the PyMol software .