Chimeric Triterpene Synthase. A Possible Model for Multifunctional Triterpene Synthase

Abstract

Two triterpene synthases, β-amyrin synthase (EC 5.4.99.−) from Panax ginseng and lupeol synthase (EC 5.4.99.−) from Arabidopsis thaliana, were used to construct a series of chimeric proteins between these two enzymes in order to investigate the region important for product specificity. Functional expression in yeast and analysis of the synthase products have revealed that chimera 1, in which the N-terminal half is β-amyrin synthase and the C-terminal half is lupeol synthase, produced both β-amyrin and lupeol in a 3:1 ratio. By dividing the whole sequence into four regions, all the possible combinations of the two synthases were constructed. Among them, chimera 7, in which only region B (the second quarter from the N-terminus) is β-amyrin synthase, produced β-amyrin and lupeol in a 4:1 ratio, indicating the importance of region B in β-amyrin formation. Another chimera, which was created by the mixed PCR method, produced β-amyrin and lupeol in a 1:4 ratio, indicating that the sequence which is important for...