Cloning, prokaryotic expression and function of the Bufo bufo gargarizans 3β-hydroxysteroid dehydrogenase (3βHSD) gene

Transcriptome Analysis and Identification of the Cholesterol Side Chain Cleavage Enzyme BbgCYP11A1 From Bufo bufo gargarizans

Bufo bufo gargarizans Cantor are precious medicinal animals in traditional Chinese medicine (TCM). Bufadienolides as the major pharmacological components are generated from the venomous glands of B. bufo gargarizans. Bufadienolides are one type of cardiac aglycone with a six-member lactone ring and have properties of antitumor, cardiotonic, tonsillitis, and anti-inflammatory. The biosynthesis of bufadienolides is complex and unclear. This study explored the transcriptome of three different tissues (skin glands, venom glands, and muscles) of B. bufo gargarizans by high-throughput sequencing. According to the gene tissue–specific expression profile, 389 candidate genes were predicted possibly participating in the bufadienolides biosynthesis pathway. Then, BbgCYP11A1 was identified as a cholesterol side chain cleaving the enzyme in engineering yeast producing cholesterol. Furthermore, the catalytic activity of BbgCYP11A1 was studied with various redox partners. Interestingly, a plant NADPH-cytochrome P450 reductase (CPR) from Anemarrhena asphodeloides showed notably higher production than BbgAdx-2A-BbgAdR from B. bufo gargarizans. These results will provide certainly molecular research to reveal the bufadienolides biosynthesis pathway in B. bufo gargarizans.

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 3β-hydroxysteroid dehydrogenase (3βHSD) and steroid 5β-reductase (SRD5β) 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 SRD5β 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-SRD5β. Bbg-SRD5β had an open reading frame of 981 bp and encoded 326 amino acids residues. The expression conditions of the recombinant Bbg-SRD5β in E. coli BL21 (DE3) harbored with pCold-Bbg-SRD5β was optimized as induction for 10 h at 15 °C with 0.1 mM IPTG. With NADPH as a cofactor, Bbg-SRD5β can reduce the Δ^4,5 double bonds of progesterone to generate dihydroprogesterone õwithout substrate inhibition effect. The catalytic rate of mutant type Bbg-SRD5β-Y132G was 1.8 times higher than that of wild type Bbg-SRD5β. Although Bbg-SRD5β was almost unable to reduce the progesterone to dihydroprogesterone after mutation of V309, the affinity of enzyme with NADPH changed significantly. Bbg-SRD5β 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-SRD5β.