Intein-Modified Xylanase for Heat-Activated Biomass Hydrolysis
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Solution Overview
Problem
The high costs and limited production capacity of enzyme loading in cellulosic biofuel production, particularly due to the challenges of biomass pretreatment and enzymatic hydrolysis, are not adequately addressed by current technologies, and in planta expression of cell wall degrading enzymes can lead to detrimental plant phenotypes impacting yield.
Innovation Solution
Development of a transgenic plant with an autohydrolytic trait using an expression vector encoding an intein-modified xylanase, where the intein is internally fused within the xylanase sequence, reducing enzyme activity and minimizing adverse plant phenotypes, thereby enhancing enzymatic hydrolysis efficiency and reducing production costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If in planta expression of cell wall degrading enzymes is used to reduce enzyme costs, then production costs are reduced, but detrimental plant phenotypes occur including stunted plant stature, poor seed set and quality, reduced fertility, and increased susceptibility to disease
Solution Approach 1:
The patent modifies the xylanase enzyme through intein fusion to alter its functional parameters. The intein-modified xylanase has reduced catalytic activity compared to the wild-type enzyme, which prevents the detrimental phenotypic effects while still providing sufficient enzymatic function for cost reduction. This parameter change in enzyme activity resolves the contradiction between production cost and plant phenotype stability.
Solution Approach 2:
The intein acts as an intermediary element between the promoter and the xylanase coding sequence. This intermediary modification allows the enzyme to be expressed in the plant while its function is modulated to avoid harmful effects. The intein serves as a mediator that enables cost-effective in planta production without the detrimental phenotypes associated with wild-type xylanase expression.
2Productivity
If high enzyme loading is used to improve hydrolysis efficiency, then biofuel production efficiency is improved, but production capacity is limited and costs increase
Solution Approach 1:
The patent enables the plant to produce its own cell wall degrading enzymes through in planta expression. This self-service approach eliminates the need for external enzyme addition and reduces dependence on external enzyme production capacity. The plant autonomously provides the enzymatic function needed for hydrolysis, thereby improving productivity while reducing the quantity of externally supplied enzymes.
3Ease of manufacture
If wild-type xylanase is expressed in plants to reduce enzyme costs, then production costs are reduced, but shriveled seed phenotypes occur impacting yield
Solution Approach 1:
The intein modification changes the functional parameters of the xylanase enzyme, reducing its catalytic activity to a level that no longer causes shriveled seed phenotypes. This parameter change allows the plant to benefit from reduced enzyme costs while maintaining normal seed development and quality, thereby resolving the contradiction between production cost and seed quality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The intein-modified xylanase in transgenic plants improves corn stover hydrolysis with or without external xylanase, maintaining xylanase activity after heat treatment, and prevents shriveled seed phenotypes, thus enhancing biofuel production efficiency and reducing enzyme costs.
Implementation Method 1
Xylanases hydrolyze hemicellulose polymers and play key roles in making cellulose more accessible to enzymatic hydrolysis
Implementation Method 2
Inteins are self-splicing peptides found within host polypeptides (exteins) in many organisms. Upon excision, inteins ligate the bordering extein polypeptide sequences back together with a peptide bond in a splicing reaction
Implementation Method 3
maintaining xylanase activity after heat treatment
Data Source
AI summary
In planta consolidated bioprocessing has the advantages of decreasing biomass pretreatment costs, utilizing excess plant protein production capacity for enzyme production, and decreasing mass transfer resistance of enzyme diffusion to its substrate. However, in planta expression of cell wall degrading (CWD) enzymes often leads to detrimental plant phenotypes that impact crop yield. To provide in planta CWD enzyme activity without any adverse phenotype, a thermostable xylanase, XynB (EC 3.2.1.8), was engineered with a thermoregulated intein, Tth-HB27 DnaE-1 (Tth intein), that controls its hydrolytic activity through conditional intein splicing. Maize plants expressing the heat inducible Tth intein-modified XynB developed normally, yet possessed enhanced post harvest glucose production from dried corn stover. Expression of CWD enzymes as dormant, intein-modified proteins that can be activated by heat treatment after harvest provides the basis for developing a novel cellulosic processing trait in plants.