Double-Immobilized Yeast Catalyst for Low-Cost Rebaudioside Synthesis
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Solution Overview
Problem
Existing methods for rebaudioside biosynthesis face high production costs, low substrate conversion and product accumulation, and inefficient enzyme utilization due to enzyme inactivation and difficult recovery, hindering large-scale industrial production.
Innovation Solution
A method for constructing double immobilized recombinant yeast engineering bacteria using a multi-enzyme complex and bacterial vector-free self-immobilization, enabling efficient synthesis of rebaudioside with reduced costs and improved enzyme activity through a self-sedimentation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If traditional plant extraction method is used to obtain rebaudioside, then rebaudioside can be extracted from stevia leaves, but the process is cumbersome, polluted seriously and expensive
Solution Approach 1:
The patent replaces the traditional mechanical plant extraction method with a biological enzyme conversion system using recombinant yeast. The yeast cells express multiple enzymes (UGT76G1, UGT85A2, SUS) that catalyze the conversion of stevioside and rebaudioside A to rebaudioside D and M through glycosylation reactions, eliminating the need for complex extraction processes
Solution Approach 2:
The patent changes the chemical parameters of the reaction system by using enzymatic catalysis at mild conditions (30-40°C, pH 6.5-7.5) compared to traditional extraction requiring organic solvents and high temperatures. The enzyme system achieves high conversion efficiency with substrate conversion rates exceeding 90%
2Productivity
If expensive substrates and donor substrates are used in biological enzyme conversion, then rebaudioside synthesis can proceed, but production cost becomes high
Solution Approach 1:
The patent implements a self-sustaining substrate regeneration system where sucrose phosphorylase (SUS) converts sucrose to glucose and UDP-glucose, providing the donor substrate for glycosylation reactions. This eliminates the need to add expensive external UDP-glucose, as the system regenerates it continuously from inexpensive sucrose
Solution Approach 2:
The patent changes the substrate economy by using abundant, inexpensive substrates (stevioside, rebaudioside A, and sucrose) instead of rare and expensive substrates. The substrate conversion efficiency exceeds 90%, and the system achieves high productivity with production costs reduced to below 50 yuan/kg
3Productivity
If free enzymes are used in co-catalysis, then multiple enzymes can work together, but enzyme recovery and reuse become difficult and enzyme activity decreases over time
Solution Approach 1:
The patent uses yeast cell walls as an intermediary carrier to immobilize multiple enzymes (UGT76G1, UGT85A2, SUS) on the cell surface. The cell wall acts as a natural support matrix that maintains enzyme activity while enabling easy separation and reuse of the catalytic system through centrifugation or filtration
Solution Approach 2:
The patent creates a composite catalytic system where enzymes are integrated with yeast cell walls to form whole-cell biocatalysts. This composite structure combines the catalytic function of multiple enzymes with the structural stability and ease of handling of yeast cells, achieving both high productivity and reliability
4Reliability
If intracellular enzymes are used for substrate conversion, then enzyme protection is provided, but product transport across membranes is hindered and accumulation is reduced
Solution Approach 1:
The patent inverts the traditional approach by moving enzymes from the intracellular environment to the extracellular cell surface. The enzymes are anchored to the yeast cell wall with their active sites exposed to the external environment, allowing direct access to substrates and immediate release of products without membrane transport barriers
Solution Approach 2:
The patent segments the catalytic function from the cellular metabolism by expressing enzymes as surface-displayed fusion proteins with cell wall anchoring domains. This separation allows the enzymes to function independently on the cell surface while the yeast cell provides structural support and protection
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 method significantly reduces production costs by using abundant substrates, enhances enzyme activity, and allows for multiple reuse of the whole cell catalyst, achieving efficient and sustainable rebaudioside synthesis.
Implementation Method 1
linking a fragment 1 and a fragment 2 to a plasmid Episomal Saccharomyces cerevisiae-URA3 gene (PESC-URA) vector to obtain a recombinant PESC-URA vector; linking a fragment 3 to a plasmid RS424 (PRS424) vector to obtain a recombinant plasmid RS424 vector, wherein the fragment 1 is a surface display scaffold protein expression cassette included by a signal peptide, a yeast cell wall anchor protein, and an adhesion domain Cohesion
Implementation Method 2
constructing a bacterial vector-free self-immobilization module: integrating a fragment 4 into a yeast genome, wherein the fragment 4 is a vector-free self-immobilization expression cassette included by a promoter and a flocculation gene
Implementation Method 3
achieving efficient synthesis of rebaudioside with reduced costs and improved enzyme activity through a self-sedimentation process
Implementation Method 4
the fragment 3 is a multi-enzyme complex expression cassette included by promoters, a signal peptide, and an anchor domain Dockerin carrying enzyme subunits
Implementation Method 5
Biological enzyme conversion method is the most technologically advantageous sustainable alternative strategy to achieve rebaudioside biosynthesis
Data Source
AI summary
A construction method of double immobilized recombinant yeast engineering bacteria, engineering bacteria, a catalyst and an application in synthesis of rebaudioside. In the present invention, yeast is used as the chassis cell, an ordered self-assembled multi-enzyme cascade surface display system is constructed, and carrier-free immobilization is coupled with uridine piphosphate glucose (UDPG) in-situ regeneration technology, resulting in a novel yeast whole cell catalyst with double immobilization of enzymes and bacteria. The catalyst uses cheap steviol glycoside (St) and rebaudioside A (Reb A) as substrates, and can synthesize rebaudioside (Reb D/M) in an efficient and economical one-pot method without additional addition of expensive UDPG. The synthesis process does not require cumbersome operations including cell disruption, enzyme separation, purification and immobilization, and avoids bottleneck problems in the related art including material transmembrane transport resistance, mass transfer resistance and product hydrolysis by intracellular enzyme. The catalyst has reusability, and can realize continuous and high-intensity rebaudioside biosynthesis through strain rejuvenation, which provides strong technical support for its industrial application.