1xnk
From Proteopedia
|
Beta-1,4-xylanase from Chaetomium thermophilum complexed with methyl thioxylopentoside
Overview
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.m. The binding constants determined by MS, titration experiments were in the range 10(4)-10(3) M-1, decreasing in the, series of S-Xyl5-Me>or=S-Xyl4-Me>S-Xyl3-Me. In contrast, S-Xyl2-Me did not, bind to any xylanase at the initial concentration of 5-200 microM, indicating increasing affinity with increasing number of xylopyranosyl, units, with a minimum requirement of three. The crystal structures of, CTX-inhibitor complexes gave interesting insights into the binding., Surprisingly, none of the inhibitors occupied any of the aglycone subsites, of the active site. The binding to only the glycone subsites is, nonproductive for catalysis, and yet this has also been observed for other, family 11 xylanases in complex with beta-d-xylotetraose [Wakarchuk WW, Campbell RL, Sung WL, Davoodi J & Makoto Y (1994) Protein Sci3, 465-475, and Sabini E, Wilson KS, Danielsen S, Schulein M & Davies GJ (2001) Acta, CrystallogrD57, 1344-1347]. Therefore, the role of the aglycone subsites, remains controversial despite their obvious contribution to catalysis.
About this Structure
1XNK is a Single protein structure of sequence from Chaetomium thermophilum with SO4 and XS2 as ligands. Active as Endo-1,4-beta-xylanase, with EC number 3.2.1.8 Full crystallographic information is available from OCA.
Reference
Determination of thioxylo-oligosaccharide binding to family 11 xylanases using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry and X-ray crystallography., Janis J, Hakanpaa J, Hakulinen N, Ibatullin FM, Hoxha A, Derrick PJ, Rouvinen J, Vainiotalo P, FEBS J. 2005 May;272(9):2317-33. PMID:15853815
Page seeded by OCA on Sun Nov 25 02:32:14 2007
