A thermostable shikimate 5-dehydrogenase from the archaeon Archaeoglobus fulgidus

Shikimate 5-dehydrogenase (SKDH; EC 1.1.1.25) catalyzes the reversible reduction of 3-dehydroshikimate to shikimate and is a key enzyme in the aromatic amino acid biosynthesis pathway. The shikimate 5-dehydrogenase gene, aroE, from Archaeoglobus fulgidus was cloned and overexpressed in Escherichia coli. The recombinant enzyme purified as a homodimer and yielded a maximum specific activity of 732 U/mg at 87°C (with NADP ⁺ as coenzyme). Apparent K _m values for shikimate, NADP ⁺, and NAD ⁺ were estimated at 0.17 ± 0.03 mM, 0.19 ± 0.01 mM, and 11.4 ± 0.4 mM, respectively. The half-life of the A. fulgidus SKDH is 2 h at the assay temperature (87°C) and 17 days at 60°C. Addition of 1 M NaCl or KCl stabilized the enzyme's half-life to ∼70 h at 87°C and ∼50 days at 60°C. This work presents the first kinetic analysis of an archaeal SKDH.