A novel bifunctional aspartate kinase-homoserine dehydrogenase from the hyperthermophilic bacterium, Thermotoga maritima

• Published in: Bioscience, biotechnology, and biochemistry biotechnology, and biochemistry, 2018-12, Vol.82 (12), p.2084-2093
• Main Authors: Ohshida, Tatsuya, Koba, Kohei, Hayashi, Junji, Yoneda, Kazunari, Ohmori, Taketo, Ohshima, Toshihisa, Sakuraba, Haruhiko
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Aspartate kinase; Aspartic Acid - metabolism; Aspartokinase Homoserine Dehydrogenase - chemistry; Aspartokinase Homoserine Dehydrogenase - genetics; Aspartokinase Homoserine Dehydrogenase - metabolism; bifunctional enzyme; Biocatalysis; Electrophoresis, Polyacrylamide Gel; Enzyme Stability; Escherichia coli - genetics; homoserine dehydrogenase; Hot Temperature; Hydrogen-Ion Concentration; hyperthermophile; Kinetics; Protein Conformation; Recombinant Proteins - genetics; Sequence Homology, Amino Acid; Thermotoga maritima; Thermotoga maritima - enzymology; Threonine - metabolism
• ISSN: 0916-8451; 1347-6947
• DOI: 10.1080/09168451.2018.1511365

The orientation of the three domains in the bifunctional aspartate kinase-homoserine dehydrogenase (AK-HseDH) homologue found in Thermotoga maritima totally differs from those observed in previously known AK-HseDHs; the domains line up in the order HseDH, AK, and regulatory domain. In the present study, the enzyme produced in Escherichia coli was characterized. The enzyme exhibited substantial activities of both AK and HseDH. L-Threonine inhibits AK activity in a cooperative manner, similar to that of Arabidopsis thaliana AK-HseDH. However, the concentration required to inhibit the activity was much lower (K 0.5  = 37 μM) than that needed to inhibit the A. thaliana enzyme (K 0.5  = 500 μM). In contrast to A. thaliana AK-HseDH, Hse oxidation of the T. maritima enzyme was almost impervious to inhibition by L-threonine. Amino acid sequence comparison indicates that the distinctive sequence of the regulatory domain in T. maritima AK-HseDH is likely responsible for the unique sensitivity to L-threonine. Abbreviations: AK: aspartate kinase; HseDH: homoserine dehydrogenase; AK-HseDH: bifunctional aspartate kinase-homoserine dehydrogenase; AsaDH: aspartate-β-semialdehyde dehydrogenase; ACT: aspartate kinases (A), chorismate mutases (C), and prephenate dehydrogenases (TyrA, T). The bifunctional aspartate kinase-homoserine dehydrogenase (AK-HseDH) from Thermotoga maritima is a novel type of the L-threonine-sensitive AK-HseDH.