Reconstitution of prenyltransferase activity on nanodiscs by components of the rubber synthesis machinery of the Para rubber tree and guayule

Prenyltransferases mediate the biosynthesis of various types of polyisoprene compound in living organisms. Natural rubber (NR) of the Para rubber tree (Hevea brasiliensis) is synthesized as a result of prenyltransferase activity, with the proteins HRT1, HRT2, and HRBP having been identified as candidate components of the rubber biosynthetic machinery. To clarify the contribution of these proteins to prenyltransferase activity, we established a cell-free translation system for nanodisc-based protein reconstitution and measured the enzyme activity of the protein-nanodisc complexes. Cell-free synthesis of HRT1, HRT2, and HRBP in the presence of asolectin nanodiscs revealed that all three proteins were membrane associated. A complex of HRT1 and HRBP formed as a result of co-expression of the two proteins in the presence of nanodiscs manifested marked polyisoprene synthesis activity, whereas neither HRT1, HRT2, or HRBP alone nor a complex of HRT2 and HRBP exhibited such activity. Similar analysis of guayule (Parthenium argentatum) proteins revealed that three HRT1 homologs (CPT1-3) manifested prenyltransferease activity only if co-expressed with the homolog of HRBP (CBP). Our results thus indicate that the core prenyltransferase of the rubber biosynthetic machinery of both the Para rubber tree and guayule is formed by the assembly of heterologous subunits (HRT1 and HRBP in the former species).