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Understanding the structural basis for substrate and inhibitor recognition in eukaryotic GH11 xylanases
Maria Vardakou1, Claire Dumon, James W Murray
1Institute for Cell and Molecular Biosciences, Newcastle University, The Medical School, Framlington Place, Newcastle upon Tyne NE2 4HH, UK.
Journal of Molecular Biology
|December 15, 2007
Summary
This study reveals how glycoside hydrolase family 11 (GH11) xylanases break down decorated xylans and why some fungal GH11 enzymes resist inhibition. Structural insights explain high catalytic activity and XIP-I resistance in these important enzymes.
Area of Science:
- Biochemistry and enzymology
- Structural biology
- Microbial biotechnology
Background:
- Endo-beta1,4-xylanases (xylanases) are crucial enzymes for degrading xylan, a major plant cell wall polysaccharide.
- Glycoside hydrolase family 11 (GH11) xylanases are extensively studied, yet mechanisms of decorated xylan hydrolysis, catalytic activity variations, and inhibition by wheat protein XIP-I remain unclear.
- Understanding these mechanisms is vital for applications in biofuel production and biomass conversion.
Purpose of the Study:
- To elucidate the mechanism of decorated xylan hydrolysis by GH11 xylanases.
- To determine the structural basis for high catalytic activity in Neocallimastix patriciarum xylanase NpXyn11A.
- To investigate the structural reasons for the differential inhibition of fungal GH11 xylanases by XIP-I.
Main Methods:
- Crystal structure determination of Neocallimastix patriciarum xylanase NpXyn11A.
- Crystal structure determination of a second GH11 xylanase, EnXyn11A, complexed with ferulic acid-1,5-arabinofuranose-alpha1,3-xylotriose (FAX(3)).
- Biochemical characterization of NpXyn11A, including catalytic activity and inhibition assays.
Main Results:
- The crystal structure of EnXyn11A-FAX(3) reveals solvent exposure at subsites -3 and +2, accommodating decorated xylose residues and indicating the ferulated arabinofuranose side chain as a potential specificity determinant.
- The structure of NpXyn11A shows extended potential -3 and +3 subsites, correlating with its unusually high catalytic activity.
- NpXyn11A's resistance to XIP-I is complex and not solely due to insertions in the loop between beta strands 11 and 12.
Conclusions:
- Structural insights into GH11 xylanases provide a mechanistic understanding of decorated xylan hydrolysis and substrate specificity.
- The extended active site cleft of NpXyn11A is likely responsible for its high catalytic efficiency.
- The complex structural basis for XIP-I resistance in NpXyn11A requires further investigation.
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