Plant progesterone 5beta-reductase is not homologous to the animal enzyme. Molecular evolutionary characterization of P5betaR from Digitalis purpurea

• Published in: Phytochemistry (Oxford) Vol. 68; no. 6; pp. 853 - 864
• Main Authors: Gavidia, Isabel, Tarrío, Rosa, Rodríguez-Trelles, Francisco, Pérez-Bermúdez, Pedro, Seitz, H Ulrich
• Format: Journal Article
• Language: English
• Published: England 01.03.2007
• Subjects: Amino Acid Sequence; Animals; Base Sequence; Digitalis - enzymology; Digitalis - genetics; DNA, Complementary - genetics; DNA, Complementary - isolation & purification; Electrophoresis, Polyacrylamide Gel; Evolution, Molecular; Gas Chromatography-Mass Spectrometry; Gene Expression Profiling; Models, Chemical; Molecular Sequence Data; Molecular Structure; Phylogeny; Plant Proteins - genetics; Plant Proteins - metabolism; Progesterone - chemistry; Progesterone - metabolism; Progesterone Reductase - genetics; Progesterone Reductase - metabolism; Recombinant Fusion Proteins - chemistry; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Reverse Transcriptase Polymerase Chain Reaction; Sequence Homology, Amino Acid
• ISSN: 0031-9422; 1873-3700

Plants of the genus Digitalis produce cardiac glycosides, i.e. digoxin, which are widely used for congestive heart failure. Progesterone 5beta-reductase (P5betaR) is a key enzyme in the biosynthesis of these natural products. Here, we have carried out the purification and partial amino acid sequencing of the native P5betaR from foxglove (Digitalis purpurea), and isolated a cDNA encoding this enzyme. Similarly to other steroid 5beta-reductases, the recombinant P5betaR catalyzes the stereospecific reduction of the Delta(4)-double bond of several steroids with a 3-oxo,Delta(4,5) structure. The gene encoding P5betaR is expressed in all plant organs, and maximally transcribed in leaves and mature flowers. P5betaR belongs to the short-chain dehydrogenase/reductase (SDR) superfamily, bearing no structural homology to its mammalian counterpart, which is a member of the aldo-keto reductase (AKR) superfamily. A similar situation occurs with 3beta-hydroxy-Delta(5)-steroid dehydrogenase (3betaHSD), the gene immediately preceding P5betaR in the cardenolide pathway, which suggests that the entire route has evolved independently in animals and plants. P5betaR is retained only in plants, where it is ubiquitous, and a few distantly related bacterial lineages after its diversification from the last universal common ancestor. Evolutionary conserved changes in its putative active site suggest that plant P5betaR is a member of a novel subfamily of extended SDRs, or a new SDR family.