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Engineering lower inhibitor affinities in beta-D-xylosidase
Zhanmin Fan1, Ling Yuan, Douglas B Jordan
1Kentucky Tobacco Research and Development Center, Department of Plant and Soil Sciences, University of Kentucky, Lexington, KY 40546, USA.
Applied Microbiology and Biotechnology
|November 19, 2009
Summary
Researchers engineered a more efficient beta-D-xylosidase (SXA) enzyme for bioethanol production. The modified enzyme shows reduced inhibition by D-xylose and D-glucose, improving its performance in lignocellulose saccharification.
Area of Science:
- Biochemistry
- Enzymology
- Biotechnology
Background:
- Beta-D-xylosidases hydrolyze xylooligosaccharides into D-xylose residues.
- The enzyme SXA from Selenomonas ruminantium is highly active but inhibited by D-xylose and D-glucose.
- Enhanced enzyme inhibition constants (Kᵢ) are crucial for efficient lignocellulose saccharification in bioethanol production.
Purpose of the Study:
- To develop a high-throughput screening method to identify SXA variants with reduced product inhibition.
- To engineer SXA for improved performance in lignocellulose saccharification for bioethanol production.
Main Methods:
- A two-tier high-throughput screen was developed to select for active SXA variants with higher Kᵢ values.
- An SXA enzyme library was created using error-prone PCR and screened using the developed method.
- Site-directed mutagenesis and kinetic analyses were performed to characterize enzyme variants.
Main Results:
- Screening of approximately 5,900 SXA enzyme library members identified improved variants.
- One variant, SXA-C3, exhibited a threefold increase in Kᵢ for D-xylose and a twofold increase for D-glucose.
- The W145G mutation was identified as a key contributor to the reduced monosaccharide affinity, primarily affecting subsite +1 binding.
Conclusions:
- Engineered SXA variants demonstrate significantly reduced product inhibition.
- The modified SXA enzyme shows enhanced potential for industrial applications, particularly in lignocellulose saccharification for bioethanol production.
- Understanding active site dynamics, specifically subsite interactions, is critical for enzyme engineering.
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