Main content area

Initiation of rubber biosynthesis: In vitro comparisons of benzophenone-modified diphosphate analogues in three rubber-producing species

Xie, Wenshuang, McMahan, Colleen M., DeGraw, Amanda J., Distefano, Mark D., Cornish, Katrina, Whalen, Maureen C., Shintani, David K.
Phytochemistry 2008 v.69 no.14 pp. 2539
Ficus elastica, Hevea brasiliensis, Parthenium argentatum, rubber, isoprenoids, biosynthesis, benzophenone
Natural rubber, cis-1,4-polyisoprene, is a vital industrial material synthesized by plants via a side branch of the isoprenoid pathway by the enzyme rubber transferase. While the specific structure of this enzyme is not yet defined, based on activity it is probably a cis-prenyl transferase. Photoactive functionalized substrate analogues have been successfully used to identify isoprenoid-utilizing enzymes such as cis- and trans-prenyltransferases, and initiator binding of an allylic pyrophosphate molecule in rubber transferase has similar features to these systems. In this paper, a series of benzophenone-modified initiator analogues were shown to successfully initiate rubber biosynthesis in vitro in enzymatically-active washed rubber particles from Ficus elastica, Hevea brasiliensis and Parthenium argentatum. Rubber transferases from all three species initiated rubber biosynthesis most efficiently with farnesyl pyrophosphate. However, rubber transferase had a higher affinity for benzophenone geranyl pyrophosphate (Bz-GPP) and dimethylallyl pyrophosphate (Bz-DMAPP) analogues with ether-linkages than the corresponding GPP or DMAPP. In contrast, ester-linked Bz-DMAPP analogues were less efficient initiators than DMAPP. Thus, rubber biosynthesis depends on both the size and the structure of Bz-initiator molecules. Kinetic studies thereby inform selection of specific probes for covalent photolabeling of the initiator binding site of rubber transferase.