The 3-Oxoacyl-(Acyl-Carrier-Protein) Reductase HSD-X1 of Pseudomonas Citronellolis SJTE-3 Catalyzes the Conversion of 17β-estradiol to Estrone

Background: Pseudomonas citronellolis SJTE-3 can efficiently degrade 17 beta-estradiol (E2) and other estrogenic chemicals. However, the enzyme responsible for E2 metabolism within strain SJTE-3 has remained unidentified. Objective: Here, a novel 3-oxoacyl-(acyl-carrier protein) (ACP) reductase, HSD-X1 (WP_009617962.1), was identified in SJTE-3 and its enzymatic characteristics for the transformation of E2 were investigated. Methods: Multiple sequence alignment and homology modelling were used to predict the protein structure of HSD-X1. The concentrations of different steroids in the culture of recombinant strains expressing HSD-X1 were determined by high performance liquid chromatography. Additionally, the transcription of hsd-x1 gene was investigated using reverse transcription and quantitative PCR analysis. Heterologous expression and affinity purification were used to obtain recombinant HS-D-X1. Results: The transcription of hsd-x1 gene in P. citronellolis SJTE-3 was induced by E2. Multiple sequence alignment (MSA) indicated that HSD-X1 contained the two consensus regions and conserved residues of short-chain dehydrogenase/reductases (SDRs) and 17 beta-hydroxysteroid dehydrogenases (17 beta-HSDs). Over-expression of hsd-x1 gene allowed the recombinant strain to degrade E2. Recombinant HSD-X1 was purified with a yield of 22.15 mg/L and used NAD(+) as its cofactor to catalyze the oxidization of E2 into estrone (E1) while exhibiting a K-m value of 0.025 +/- 0.044 mM and a V-max value of 4.92 +/- 0.31 mM/min/mg. HSD-X1 could tolerate a wide range of temperature and pH, while the presence of divalent ions exerted little influence on its activity. Further, the transformation efficiency of E2 into E1 was over 98.03% across 15 min. Conclusion: Protein HSD-X1 efficiently catalyzed the oxidization of E2 and participated in estrogen degradation by P. citronellolis SJTE-3.