Cloning and Characterization of Two cDNA Sequences Coding Squalene Synthase Involved in Glycyrrhizic Acid Biosynthesis in Glycyrrhiza uralensis

Glycyrrhiza uralensis are widely used in Chinese medicine for the functions of relieving cough, clearing heat and detoxicating. They are also used as food additives and industry materials. There are various components with different pharmacological activities in G. uralensis, among them glycyrrhizic acid is believed as an indicator component to characterize the quality of this herb. In the present study, two cDNA sequences coding squalene synthase (SQS1 and SQS2) involved in glycyrrhizic acid biosynthesis in G. uralensis were cloned and expressed in Escherichia coli as fusion proteins, which showed the similar activity as SQS isolated from other species to catalyze farnesyl diphosphate (FPP) into squalene (SQ). Because SQS is a key enzyme in glycyrrhizic acid metabolic pathway in G. uralensis, this work is significant for further studies concerned with exploring the molecular mechanism of biosynthesis of glycyrrhizic acid and improving the quality of G. uralensis.