Determination of thioxylo-oligosaccharide binding to family 11 xylanases using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry and X-ray crystallography.

Noncovalent binding of thioxylo-oligosaccharide inhibitors, methyl 4-thio-alpha-xylobioside (S-Xyl2-Me), methyl 4,4II-dithio-alpha-xylotrioside (S-Xyl3-Me), methyl 4,4II,4III-trithio-alpha-xylotetroside (S-Xyl4-Me), and methyl 4,4II,4III,4IV-tetrathio-alpha-xylopentoside (S-Xyl5-Me), to three family 11 endo-1,4-beta-xylanases from Trichoderma reesei (TRX I and TRX II) and Chaetomium thermophilum (CTX) was characterized using electrospray ionization Fourier transform ion cyclotron resonance (FT-ICR) MS and X-ray crystallography. Ultra-high mass-resolving power and mass accuracy inherent to FT-ICR allowed mass measurements for noncovalent complexes to within |DeltaM|average of 2 p.p.