Characterization of cis-prenyltransferases from the rubber producing plant Hevea brasiliensis heterologously expressed in yeast and plant cells

A precise mechanism for the biosynthesis of natural rubber has not yet been elucidated. The cisprenyltransferase (cPT), HRT2, identified from latex of Hevea brasiliensis, is thought to be a key enzyme in the biosynthesis of natural rubber. This is due to the observation that recombinant HRT2, expressed in Escherichia coli, is significantly activated in the presence of a centrifuged latex fraction, resulting in the formation of polyisoprenes corresponding to natural rubber. The precise enzymatic characterization of cPT function for HRT2, however, has not been investigated because HRT2 expressed in E. coli does not exhibit significant activity independently. Herein, the enzymatic characterization of HRTs expressed in eukaryotic cell systems is reported. Both HRT2 and HRT1, another cPT from Hevea latex, expressed in Saccharomyces cerevisiae and Arabidopsis T87 cultured cells showed distinct cPT activity, producing polyisoprenoids with chain-lengths of C_80-100, although failing to catalyze the formation of natural rubber. The chain lengths of the HRT1/HRT2 products were not altered by the addition of centrifuged latex fractions, and the HRT1/HRT2 expressed in yeast competed with the rubber transferase activity of the latex fraction. These results indicate that HRT1/HRT2 requires additional cofactors from the eukaryotic cells to produce distinct cPT activity, and that latex specific co-factor(s) may be required to enable HRT1/HRT2 rubber transferase activity.