L-valine

L-Valine is a branched-chain amino acid that is synthesized through a metabolic pathway utilizing 2-ketoisovalerate (KIV) as a direct intermediate [94]. The biosynthesis of this amino acid involves enzymes such as acetohydroxy acid synthase (AHAS) and acetolactate synthase (AlsS), which are responsible for early steps in the branched-chain amino acid pathway [94].

The L-valine biosynthetic pathway serves as a foundational platform for the microbial production of biofuels and commodity chemicals [94]. A key engineering approach involves diverting the pathway intermediate 2-ketoisovalerate to produce isobutanol through the heterologous expression of 2-ketoacid decarboxylase (Kdc) and alcohol dehydrogenase (Adh) [94, 98]. Strategies to optimize L-valine production include systems metabolic engineering, which integrates transcriptome profiling and in silico genome-scale metabolic network simulations to identify genetic targets for modification [200, 363]. Additionally, guided evolution and adaptive laboratory evolution are utilized as strategies to develop high-performing microbial cell factories by optimizing metabolic flux and host fitness [363].