Abstract
In bacteria, threonine dehydratases could convert L-threonine to 2-ketobutyrate. Some threonine dehydratases contain only a catalytic domain, while others contain an N-terminal catalytic domain and a C-terminal regulatory domain composed of one or two ACT-like subdomains. However, the role of the ACT-like subdomain in threonine dehydratases is not clear. Here, nine different bacterial threonine dehydratases were studied. Three of the nine contain no ACT-like subdomain, four of them contain a single ACT-like subdomain, and two of them contain two ACT-like subdomains. The nine genes encoding these threonine dehydratases were individually overexpressed in E. coli BL21(DE3), and the enzymes were purified to homogeneity. Activities of the purified enzymes were analyzed after incubation at different temperatures and different pHs. The results showed that threonine dehydratases with a single ACT-like subdomain are more stable at higher temperatures and a broad range of pH than those without ACT-like subdomain or with two ACT-like subdomains. Furthermore, the specific activity of threonine dehydratases increases with the increase of the number of ACT-like subdomains they contain. The results suggest that the ACT-like subdomain plays an important role in bacterial threonine dehydratases.
Highlights
Bacterial threonine dehydratase (TD) converts L-threonine to 2ketobutyrate
biosynthetic threonine dehydratase (BTD) functions in the biosynthetic pathway of Lisoleucine when bacteria grow under aerobic conditions, and usually contains an N-terminal catalytic domain and a C-terminal regulatory domain
catabolic threonine dehydratase (CTD) contains only the catalytic domain, and plays a role in the degradation of L-threonine to propionate when bacteria grow under anaerobic conditions [1], its activity is activated by AMP and CMP [2]
Summary
Bacterial threonine dehydratase (TD) converts L-threonine to 2ketobutyrate. There are usually two types of TD: biosynthetic threonine dehydratase (BTD) and catabolic threonine dehydratase (CTD) (Fig. 1). BTD encoded by the gene ilvA in Escherichia coli contains two ACT-like subdomains in its Cterminal regulatory domain. BTD encoded by ilvA in Bacillus subtilis, contains only one ACT-like subdomain in its C-terminal regulatory domain, and is inhibited by L-isoleucine or by high concentrations of L-valine [5].
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