7-Oxo-lithocholic acid (7-oxo-LCA) is a key precursor for the enzymatic synthesis of the therapeutic bile acid ursodeoxycholic acid (UDCA). Chenodeoxycholic acid (CDCA) can be readily converted to 7-oxo-LCA by the 7α-hydroxysteroid dehydrogenase (7α-HSDH). However, the poor substrate tolerance of the current 7α-HSDH limits their practical applications. In this study, a new and natively NAD(+)-dependent Sm7α-HSDH from Shewanella morhuae was identified, which exhibited a better substrate tolerance compared with other 7α-HSDHs. The purified Sm7α-HSDH showed a high oxidative activity of 281 U mg⁻¹_protein toward CDCA, with a catalytic efficiency (k_cat/K_m) of 7.47 × 10³ mM⁻¹ s⁻¹. In a preparative biotransformation (100 mL scale), 200 mM (∼80 g L⁻¹) CDCA was almost completely oxidized to 7-oxo-LCA in 1 h, with a 78% isolated yield and a space-time yield (STY) of up to 1418 g L⁻¹ d⁻¹, which is so far the highest productivity for biosynthesis of 7-oxo-LCA from CDCA. These results demonstrate the great potential of Sm7α-HSDH as a promising biocatalyst for UDCA synthesis.

7-氧代-石胆酸 (7-氧代-LCA) 是酶法合成治疗性胆汁酸熊去氧胆酸 (UDCA) 的关键前体。鹅去氧胆酸 (CDCA) 可以很容易地被 7α-羟基类固醇脱氢酶 (7α-HSDH) 转化为 7-oxo-LCA。然而，目前的7α-HSDH较差的底物耐受性限制了其实际应用。在这项研究中，从希瓦氏菌中鉴定出一种新的天然 NAD(+) 依赖性Sm 7α-HSDH ，与其他 7α-HSDH 相比，它表现出更好的底物耐受性。纯化的Sm 7α-HSDH对CDCA表现出281 U mg ^-1_蛋白的高氧化活性，催化效率( k _cat /K _m )为7.47 × 10 ³ mM ^-1 s ^-1。在制备型生物转化（100 mL规模）中，200 mM（∼80 g L ^-1）CDCA在1小时内几乎完全氧化为7-oxo-LCA，分离产率和时空产率（STY）为78%高达1418 g L ^-1 d ^-1，这是迄今为止从CDCA生物合成7-oxo-LCA的最高生产率。这些结果证明了Sm 7α-HSDH 作为 UDCA 合成有前景的生物催化剂的巨大潜力。