title: In search of sustainable chemical processes: cloning, recombinant expression, and functional characterization of the 7α- and 7β-hydroxysteroid dehydrogenases from Clostridium absonum.
abstract: Nicotinamide adenine dinucleotide phosphate-dependent 7α-hydroxysteroid dehydrogenase (7α-HSDH) and 7β-hydroxysteroid dehydrogenases (7β-HSDH) from Clostridium absonum catalyze the epimerization of primary bile acids through 7-keto bile acid intermediates and may be suitable as biocatalysts for the synthesis of bile acids derivatives of pharmacological interest. C. absonum 7α-HSDH has been purified to homogeneity and the N-terminal sequence has been determined by Edman sequencing. After PCR amplifications of a gene fragment with degenerate primers, cloning of the complete gene (786 nt) has been achieved by sequencing of C. absonum genomic DNA. The sequence coding for the 7β-HSDH (783 nt) has been obtained by sequencing of the genomic DNA region flanking the 5' termini of 7α-HSDH gene, the two genes being contiguous and presumably part of the same operon. After insertion in suitable expression vectors, both HSDHs have been successfully produced in recombinant form in Escherichia coli, purified by affinity chromatography and submitted to kinetic analysis for determination of Michaelis constants (K                         (m)) and specificity constants (k                         (cat)/K                         (m)) in the presence of various bile acids derivatives. Both enzymes showed a very strong substrate inhibition with all the tested substrates. The lowest K                         (S) values were observed with chenodeoxycholic acid and 12-ketochenodeoxycholic acid as substrates in the case of 7α-HSDH, whereas ursocholic acid was the most effective inhibitor of 7β-HSDH activity.
authors.affiliation: Istituto di Chimica del Riconoscimento Molecolare, C.N.R., Via Mario Bianco 9, 20131, Milan, Italy.
authors.forename: Erica Elisa
authors.initials: EE
authors.lastname: Ferrandi
authors.forename: Giulia Maria
authors.initials: GM
authors.lastname: Bertolesi
authors.forename: Fausto
authors.initials: F
authors.lastname: Polentini
authors.forename: Armando
authors.initials: A
authors.lastname: Negri
authors.forename: Sergio
authors.initials: S
authors.lastname: Riva
authors.forename: Daniela
authors.initials: D
authors.lastname: Monti
mesh_terms: D001647:Bile Acids and Salts / Q000378:metabolism; D001711:Biotransformation; D002846:Chromatography, Affinity; D003001:Cloning, Molecular; D003013:Clostridium / Q000201:enzymology* / Q000235:genetics; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004791:Enzyme Inhibitors / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D015870:Gene Expression; D006913:Hydroxysteroid Dehydrogenases / Q000235:genetics* / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D009876:Operon; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D017422:Sequence Analysis, DNA
chemical_list: D001647:Bile Acids and Salts; D004269:DNA, Bacterial; D004791:Enzyme Inhibitors; D011994:Recombinant Proteins; D006913:Hydroxysteroid Dehydrogenases; C031932:7 beta-hydroxysteroid dehydrogenase; C025376:7 alpha-hydroxysteroid dehydrogenase