Cloning and characterization of steroid 5β-reductase from the venom gland of Bufo bufo gargarizans
Bufadienolides are the main active ingredients of Venenum Bufonis, which is a widely used traditional Chinese medicine secreted from parotoid gland and skin glands of Bufo bufo gargarizans . According to the transcriptome analysis, “cholesterol-bile acid-bufadienolidies pathway” was proposed as animal-derived bufadienolides biosynthesis pathway by us previously. In this pathway 3 β -hydroxysteroid dehydrogenase (3 β HSD) and steroid 5 β -reductase (SRD5 β ) might be the key enzymes to convert the A/B ring to cis -configuration. Therefore, as the second report of our group, here we report the cloning of the full length of SRD5 β cDNA of B. bufo gargarizans ( Bbg - SRD5β ) from the parotoid gland of B. bufo gargarizans for the first time, and site-directed mutagenesis was used to explored the character of Bbg -SRD5 β . Bbg -SRD5 β had an open reading frame of 981 bp and encoded 326 amino acids residues. The expression conditions of the recombinant Bbg -SRD5 β in E. coli BL21 (DE3) harbored with pCold- Bbg -SRD5 β was optimized as induction for 10 h at 15 °C with 0.1 mM IPTG. With NADPH as a cofactor, Bbg -SRD5 β can reduce the Δ 4,5 double bonds of progesterone to generate dihydroprogesterone õwithout substrate inhibition effect. The catalytic rate of mutant type Bbg -SRD5 β -Y132G was 1.8 times higher than that of wild type Bbg -SRD5 β . Although Bbg -SRD5 β was almost unable to reduce the progesterone to dihydroprogesterone after mutation of V309, the affinity of enzyme with NADPH changed significantly. Bbg -SRD5 β is the key enzymes to convert the A/B ring of steroid to cis -configuration, and V309 is a key site affecting the binding affinity of enzyme with NADPH, and the mutation of Y132 can adjust the catalytic rate of Bbg -SRD5 β .
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