Mutant Phosphomevalonate Decarboxylase Screening for Isopentenol Production
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Solution Overview
Problem
The conventional mevalonate (MVA) pathway for isopentenol production in E. coli is limited by high ATP requirements and toxicity of isopentenyl pyrophosphate (IPP), which inhibits growth and diverts carbon flux away from desired production, necessitating the development of more energetically efficient pathways.
Innovation Solution
A high-throughput screening platform is used to identify mutant phosphomevalonate decarboxylases (PMD) with enhanced activity, coupled to growth rates by blocking IPP production via the MEP pathway and increasing IP kinase activity, leading to improved isopentenol production through the IPP-bypass MVA pathway.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the conventional MVA pathway is used for isopentenol production, then the pathway can produce isopentenol through standard enzymatic reactions, but the ATP requirement becomes excessively high (3 ATP molecules per IPP molecule)
Solution Approach 1:
The patent extracts and removes the ATP-consuming step from the conventional MVA pathway by eliminating the PMK enzyme that catalyzes the phosphorylation of MVAP to MVAPP. This creates an alternative pathway where MVAP is directly decarboxylated to IP by PMD, bypassing the energy-intensive phosphorylation step and subsequent ATP hydrolysis, thereby reducing total ATP consumption from 3 to 2 ATP molecules per IPP equivalent produced
Solution Approach 2:
The patent inverts the conventional reaction sequence by reversing the order of decarboxylation and phosphorylation. Instead of first phosphorylating MVAP to MVAPP and then decarboxylating to IPP (which consumes 2 ATP), the inverted pathway first decarboxylates MVAP to IP (consuming 1 ATP) and then phosphorylates IP to IPP (consuming 1 ATP), but with the key difference that IP can be directly converted to isopentenol without requiring full phosphorylation to diphosphate form, effectively reducing energy consumption
2Productivity
If the conventional MVA pathway produces IPP, then isopentenol can be synthesized, but IPP accumulation becomes toxic and inhibits E. coli growth
Solution Approach 1:
The patent introduces IP (isopentenyl phosphate) as an intermediary substance that mediates between MVAP and the final isopentenol product. IP serves as a less toxic intermediate that can be directly converted to isopentenol by phosphatases, avoiding the accumulation of toxic IPP while maintaining pathway flux. This intermediary approach allows the cell to produce isopentenol without exposing itself to the harmful effects of high IPP concentrations
Solution Approach 2:
The patent extracts IPP from the pathway by using PMD to directly decarboxylate MVAP to IP instead of producing IPP through the conventional PMK-PMD sequence. This removal of IPP production eliminates the source of toxicity while the IP intermediate can be efficiently converted to the desired isopentenol product, thereby decoupling productivity from toxicity
3Productivity
If the MVA pathway is optimized for isopentenol production, then titers reach 2.2 g/L with 70% theoretical yield, but the pathway remains limited by intrinsic constraints
Solution Approach 1:
The patent changes the biochemical parameters of the pathway by introducing a mutant PMD enzyme with altered substrate specificity and enhanced activity toward MVAP. This parameter change allows the enzyme to function effectively in the alternative pathway configuration, enabling higher isopentenol titers and improving the overall adaptability of the system to different pathway designs
Solution Approach 2:
The patent creates a dynamic and flexible pathway system by using an inducible expression system and a mutant PMD enzyme that can adapt to different substrate conditions. The pathway can dynamically adjust its flux based on cellular needs and environmental conditions, providing greater versatility for engineering different production scenarios and improving overall system adaptability
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
This approach significantly increases isopentenol titers by up to 2.4-fold, reducing IPP toxicity and improving energetic efficiency, while correlating growth rates with PMD activity, thereby enhancing the productivity of the IPP-bypass pathway.
Implementation Method 1
phosphomevalonate decarboxylase (PMD) converts MVAPP to isopentenyl diphosphate (IPP) while consuming one additional ATP molecule
Implementation Method 2
mevalonate kinase (MK) phosphorylates MVA to mevalonate 5-phosphate (MVAP), which is subsequently phosphorylated to mevalonate 5-diphosphate (MVAPP, also diphosphomevalonate) by 5-phosphomevalonate kinase (PMK)
Data Source
AI summary
The present invention provides for a method to identify a second or mutant phosphomevalonate decarboxylase (PMD) with a higher PMD activity compared to a first PMD, comprising (a) culturing a medium comprising a first host cell expressing the first PMD and a second host cell expressing the second or mutant PMD wherein the first and second host cells have their respective PMD enzymatic activities coupled to the growth rates of the host cells, and (b) identifying the second host cell that has a higher growth rate than the first host cell, thereby identifying the second or mutant PMD having a higher PMD activity.