Molecular cloning and functional expression of cDNAs for Glycyrrhiza glabra squalene synthase

We have isolated two cDNAs (GgSQS1 and GgSQS2) encoding squalene synthase of Glycyrrhiza glabra L. by cross-hybridization with that of Arabidopsis thaliana squalene synthase under conditions of low stringency. Their nucleotide sequences contained an open reading frame for a polypeptide of 413 amino acids (GgSQS1) and 412 amino acids (GgSQS2), respectively. The deduced amino acid sequence of GgSQS1 exhibits 88%, 81%, 78%, 45-44%, and 45-41% identity to those of the GgSQS2, Nicotiana benthamiana, Arabidopsis thaliana, mammal, and yeast squalene synthases, respectively. To express the G. glabra enzymes in Escherichia coli, the entire coding region was subcloned into an expression vector. The cell-free extracts of E. coli transformed with the respective plasmid converted H-3-farnesyl diphosphate into squalene.