KAH Enzyme Variants for High-Yield Steviol Glycoside Biosynthesis
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Solution Overview
Problem
The production of Reb M, a high-potency sweetener derived from the stevia plant, is impractical due to its low natural abundance, necessitating improved enzymatic steps for efficient bioconversion in microorganisms.
Innovation Solution
Development of variant kaurenoic acid hydroxylase (KAH) enzymes with specific amino acid substitutions to enhance the conversion of kaurenoic acid to steviol, integrated into host cells such as yeast, enabling efficient production of steviol glycosides like Reb M.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If wild-type KAH enzyme is used in yeast, then the enzymatic step performs poorly with low conversion efficiency, but using variant KAH enzymes with specific amino acid substitutions improves conversion efficiency to >90%
Solution Approach 1:
The patent applies parameter changes by modifying the amino acid sequence of the KAH enzyme through specific substitutions (e.g., positions 69, 72, 161, 297, 466, 505, 506, 507). These sequence parameter changes result in variant enzymes with dramatically improved catalytic efficiency, achieving >90% conversion of kaurenoic acid to steviol compared to poor performance of wild-type enzyme in yeast.
2Manufacturing precision
If stevia plant is used for Reb M production, then the product has high potency and appealing flavor, but Reb M is only produced in minute quantities as a small fraction of total steviol glycoside content
Solution Approach 1:
The patent applies local quality by using variant KAH enzymes that specifically catalyze the conversion of kaurenoic acid to steviol with high efficiency and specificity. This localized enzymatic improvement at the KAH step enables selective production enhancement of desired steviol glycosides including Reb M, achieving both high quality and improved yield in microbial fermentation systems.
Solution Approach 2:
The patent applies preliminary action by optimizing the KAH enzymatic step early in the biosynthetic pathway from kaurenoic acid to steviol. By establishing high conversion efficiency at this upstream step using variant enzymes, the pathway is primed for subsequent glycosylation steps that produce Reb M, enabling efficient overall production before the compound enters the plant system.
3Productivity
If economic production of Reb M is pursued, then each enzymatic step needs high conversion efficiency (>90%), but particular enzymatic steps perform poorly with wild-type enzymes in yeast
Solution Approach 1:
The patent applies parameter changes by systematically modifying the KAH enzyme's amino acid sequence to achieve >90% conversion efficiency. These sequence parameter optimizations make the enzymatic step in yeast feasible and economically viable, transforming a poorly performing wild-type step into a high-efficiency conversion that meets industrial production requirements.
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 variant KAH enzymes achieve high efficiency in converting kaurenoic acid to steviol, significantly increasing the yield and productivity of Reb M in microbial fermentation processes.
Implementation Method 1
kaurenoic acid 13-hydroxylase (KAH) which catalyzes the conversion of ent-kaurenoic acid into steviol
Implementation Method 2
KAHs that are capable of converting kaurenoic acid to steviol with high efficiency
Data Source
AI summary
Provided herein are genetically modified host cells, compositions, and methods for improved production of steviol glycosides. The host cells are genetically modified to contain a heterologous nucleic acid that expresses novel and optimized variants of Ro.KAH. The host cell further contains one or more heterologous nucleotide sequence encoding further enzymes of a pathway capable of producing one or more steviol glycosides in the host cell. The host cells, compositions, and methods described herein provide an efficient route for the heterologous production of steviol glycosides including rebaudioside A, rebaudioside D, and rebaudioside M.