<p>The intracellular metabolic activities of microorganisms are complex, and it is difficult to systematically understand their regulatory mechanisms and efficiently obtain the required phenotypes by a single research method. Genome-scale metabolic model (GSMM) is a mathematical model used to describe the relationship between genes, proteins, and responses, and has been widely used to analyze network properties, predict cell phenotypes, guide strain design, and analyze interactions. Based on GSMM, the enzyme-constrained model constructed by integrating large-scale enzyme kinetics and proteomics data has more accurate phenotypic prediction ability. </p>
<p>In our experiments, in order to improve the yield of 5-ALA, we used an enzyme-constrained model to simulate the effects of the following strategies on the target product from a global perspective while enzymatically modifying ALAS, combined with different genetic modification methods: 1) eliminate the competition pathway; 2) strengthen the synthesis of pathway-critical genes; 3) eliminate feedback inhibition; 4) optimize cofactors. This method is helpful to screen and combine different metabolic modification targets and guide experimental design, which not only realizes the rational design of strain modification, improves the efficiency of metabolic engineering, but also comprehensively considers the impact of genetic perturbation on microbial intracellular metabolism, so as to achieve precise metabolic flux regulation. We used the enzyme-constrained model that had been constructed in <i>E. coli BL21(DE3)</i> as the initial model, and since the initial model did not include relevant reactions regarding the synthesis ec_iECBD_1354 of 5-ALA by the C4 pathway, we introduced the synthesis pathway of 5-ALA by the C4 pathway into the original model. </p>
<p>And since the transport and exchange reaction of 5-ALA is a reversible reaction, catalyzing the reversible enzymes in two directions corresponding to two different k<sub>cat</sub> values, the reverse reaction of the transport and exchange reaction of 5-ALA is also introduced into the model. </p>
<h3><b>Test</b></h3>
<p>We will tune the model to identify synthetic targets that can enhance 5-ALA. When comparing the differences in protein requirements between the cell growth stage and the product synthesis stage, 30 proteins were identified as the most demanded proteins that needed to be upregulated. While 10 proteins are classified as having reduced demand and need to be downgraded. </p>
<spanclass="figure-font">Table. 2 Increased demand for protein</span>
