title: Comamonas testosteroni 3-ketosteroid-delta 4(5 alpha)-dehydrogenase: gene and protein characterization.
abstract: Comamonas testosteroni delta 4(5 alpha)- and delta1-dehydrogenases [delta4(5alpha)- and delta1DH] are key enzymes in the degradation of steroids having an A:B ring fusion in a trans configuration. We previously reported the isolation of the delta1dh gene (P. Plesiat, M. Grandguillot, S. Harayama, S. Vragar, and Y. Michel Briand, J. Bacteriol. 173:7219-7227, 1991). In this study, the gene encoding delta 4(5 alpha)DH was cloned in Escherichia coli on a 16-kbp BamHI fragment by screening a genomic bank of C. testosteroni ATCC 17410 with a probe derived from delta1dh. Subcloning experiments in plasmid pUC19 mapped delta 4(5 alpha)dh immediately downstream of delta1dh. The enzyme was overexpressed 18-fold in cells of E. coli JM109 carrying a 2.5-kbp cloned fragment (plasmid pXE25). However, much higher levels of enzymatic activity (264-fold) were obtained in Pseudomonas putida KT2440, using pMMB208 as an expression vector. Studies with crude lysates of KT2440 showed that delta4(5alpha)DH exhibits higher specificity and higher activity toward delta  l-androstene-3,17-dione than toward the saturated derivative 5 alpha-androstane-3,17-dione. The reaction was found to be irreversible and to use efficiently typical flavoprotein electron acceptors; optimal conditions for the enzyme activity were pH 8 and 40 degrees C. Analysis of the nucleotide sequence of the insert of pXE25 revealed an open reading frame of 1,593 bp preceded by a putative ribosome-binding site and followed by a potential transcription terminator. The amino acid sequence of the deduced peptide showed a typical flavin adenine dinucleotide-binding site in its N-terminal region, confirming the flavoproteinic structure of delta 4(5 alpha)DH. The predicted molecular mass was consistent with that of the enzyme expressed in a T7 polymerase system (60 kDa). Alignment between delta 4(5 alpha)dh and delta1dh indicated that both genes, though coding for functionally related enzymes, do not derive from a common ancestor.
authors.affiliation: Laboratoire de Bactériologie, Faculté de Médecine, Besançon, France.
authors.forename: C
authors.initials: C
authors.lastname: Florin
authors.forename: T
authors.initials: T
authors.lastname: Köhler
authors.forename: M
authors.initials: M
authors.lastname: Grandguillot
authors.forename: P
authors.initials: P
authors.lastname: Plesiat
mesh_terms: D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000737:chemistry; D004926:Escherichia coli / Q000235:genetics; D006088:Gram-Negative Aerobic Bacteria / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000235:genetics*; D011994:Recombinant Proteins / Q000096:biosynthesis
chemical_list: D004269:DNA, Bacterial; D011994:Recombinant Proteins; D010088:Oxidoreductases; C022656:3-oxosteroid delta(1) dehydrogenase; D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase