Molecular cloning and characterization of the gene encoding squalene epoxidase in Panax notoginseng

Squalene epoxidase (SE) is one of the rate-limiting enzymes in the triterpene saponins biosynthetic pathway. Panax notoginseng, one of the famous medicinal plants in China, produces bioactive triterpene saponins. Here we report the P notoginseng SE, which was cloned from the root of P notoginseng by PCR. The nucleotide sequence of the ORF (GenBank accession no. DQ386734) contains 1611 nucleotides and encodes 537 amino acid residues with molecular weight of 59.14kDa and pI of 8.81. The gene has 98% identity with R ginseng but different identities with other SE fan-lilies. P notoginseng SE has a FAD function domain, NAD(P)-binding Rossmann-fold domains, hydrophobicity and 4 transmembrane helices. This SE may be a microsomal membrane-associated enzyme. Real time quantitative PCR shows that the cDNA has different expression pattern and is highly expressed in root, especially in 3-year-old root.