7beta-hydroxysteroid dehydrogenase that catalyzes the reduction of the 7-oxo group of 7-oxo-lithocholate (7-oxo-LCA), to yield ursodeoxycholate (UDCA) (PubMed:21181147, PubMed:6954878, PubMed:27006087). As C.aerofaciens is an intestinal bacterium, this enzyme probably contributes to the formation of UDCA in the human colon. UDCA is regarded as a chemopreventive beneficial secondary bile acid due to its low hydrophobicity; it protects hepatocytes and bile duct epithelial cells against necrosis and apoptosis induced by more hydrophobic secondary bile acids like deoxycholate (DCA) (Probable). This enzyme is also able to catalyze the reverse reaction, i.e. the oxidation of the 7beta-hydroxy group of UDCA to 7-oxo-LCA (PubMed:21181147, PubMed:6954878). To a lesser extent, is also active on the taurine- and glycine-conjugates of ursodeoxycholate. It is specific for NADPH/NADP(+) as the electron acceptor/donor since it is not active with NADH/NAD(+) (PubMed:6954878). In the presence of NADPH, 7beta-HSDH can also reduce dehydrocholate (PubMed:21181147). And is also able to oxidize ursocholate (PubMed:27006087). a 7beta-hydroxysteroid + NADP(+) = a 7-oxosteroid + H(+) + NADPH 7-oxolithocholate + H(+) + NADPH = NADP(+) + ursodeoxycholate 7beta-hydroxy-3,12-dioxo-5beta-cholan-24-oate + NADP(+) = dehydrocholate + H(+) + NADPH NADP(+) + ursocholate = 3alpha,12alpha-dihydroxy-7-oxo-5beta-cholanate + H(+) + NADPH kcat is 1179 min(-1) for the oxidation of ursodeoxycholate. kcat is 951 min(-1) for the reduction of 7-oxolithocholate. kcat is 875 min(-1) for the reduction of dehydrocholate. Optimum pH is 9-10 for the oxidation of ursodeoxycholate. Optimum pH is 4-6 for the reduction of 7-oxo-LCA and dehydrocholate. Is not very thermostable. The enzyme is completely inactivated at 50 degrees Celsius within 5 minutes and at 40 degrees Celsius within 400 minutes. Homodimer. Is expressed constitutively and repressed by ursodeoxycholate. The 27 C-terminal residues (residues 237-263) are absolutely required for enzymatic activity; a deletion mutant lacking this C-terminal region shows a complete absence of enzymatic activity. Could be a useful biocatalyst for the preparative production of ursodeoxycholate, an FDA-approved cholic acid derivate drug used to treat cholesterol gallstones and current sole alternative to surgical intervention. Belongs to the short-chain dehydrogenases/reductases (SDR) family.