Molecular Evolution of Threonine Dehydratase in Bacteria

Abstract

Threonine dehydratase converts L-threonine to 2-ketobutyrate. Several threonine dehydratases exist in bacteria, but their origins and evolutionary pathway are unknown. Here we analyzed all the available threonine dehydratases in bacteria and proposed an evolutionary pathway leading to the genes encoding three different threonine dehydratases CTD, BTD1 and BTD2. The ancestral threonine dehydratase might contain only a catalytic domain, but one or two ACT-like subdomains were fused during the evolution, resulting BTD1 and BTD2, respectively. Horizontal gene transfer, gene fusion, gene duplication, and gene deletion may occur during the evolution of this enzyme. The results are important for understanding the functions of various threonine dehydratases found in bacteria.

The σB-dependent regulatory sRNA Rli47 represses isoleucine biosynthesis inListeria monocytogenesthrough a direct interaction with theilvAtranscript

“…The ilvA gene encodes threonine deaminase (TD), which is the first key enzyme on the L-isoleucine biosynthetic pathway that catalyzes the deamination of threonine to produce alphaketobutyrate, water and ammonia [22,23]. To investigate the contribution of Rli47 to L-isoleucine biosynthesis, L. monocytogenes EGD-e wild-type, ΔsigB and Δrli47 strains were grown in DM either with (DM) or without (DM-ile) isoleucine supplementation (Figure 6(a)).…”

“…Here we report predicted binding targets for Rli47 using an in silico and in vivo analysis of its secondary structure, and we confirmed its binding in vitro to a target mRNA associated with branched-chain amino acid (BCAA) biosynthesis. The data presented show that Rli47 can base-pair through a singlestranded CU-rich loop with the Shine-Dalgarno (SD) region of the ilvA mRNA, which encodes threonine deaminase (TD), the first key enzyme on the L-isoleucine (ile) biosynthetic pathway that catalyzes the deamination of L-threonine to produce alpha-ketobutyrate [22,23]. This interaction negatively regulates the expression of ilvA, reducing the threonine deaminase enzymatic activity.…”

Molecular evolution of acetohydroxyacid synthase in bacteria

“…With the divergence of new species, one or two of the genes encoding for AHAS and AHAS I‐II were deleted from the genome. The similar deletion events along with new species generation were common, these were also found in other enzymes, such as threonine dehydratase in isoleucine biosynthesis pathway and UDP‐2,3‐diacylglucosamine pyrophosphatase in Kdo 2 lipid A biosynthesis pathway (Opiyo, Pardy, Moriyama, & Moriyama, ; Yu et al., ). Finally, among the species of γ‐proteobacteria, the gene AHAS II might be duplicated, generating AHAS I.…”

“…It had a single AHAS, but it was clustered in AHAS II‐L. The exceptions in Xanthomonadaceae could also be observed in the evolution model of aspartokinases and threonine dehydratases (Fondi, Brilli, & Fani, ; Yu et al., ). This exception may cause by horizontal gene transfer or delete genes in the genome.…”

“…From an evolution point of view, enzymes like AHAS which could simultaneously participate in two pathways are particularly significant. Threonine dehydratase, another key enzyme in the biosynthetic pathway of L‐isoleucine, has been reported to occur horizontal gene transfer, gene fusion, duplication and deletion during the evolution (Yu, Li, & Wang, ). The leu genes in the BCAA biosynthetic pathway are paralogous to lys and arg genes, and their interrelationships might due to a cascade of duplication of ancestral genes which could catalyze different kinds of substrates (Fondi, Brilli, Emiliani, Paffetti, & Fani, ).…”