Research & Teaching Faculty

Default Header Image

Cloning and Characterization of Oxidosqualene Cyclases from Kalanchoe daigremontiana: ENZYMES CATALYZING UP TO 10 REARRANGEMENT STEPS YIELDING FRIEDELIN AND OTHER TRITERPENOIDS.

TitleCloning and Characterization of Oxidosqualene Cyclases from Kalanchoe daigremontiana: ENZYMES CATALYZING UP TO 10 REARRANGEMENT STEPS YIELDING FRIEDELIN AND OTHER TRITERPENOIDS.
Publication TypeJournal Article
Year of Publication2010
AuthorsWang, Z, Yeats, T, Han, H, Jetter, R
JournalJournal of Biological Chemistry
Volume285
Pagination29703 - 29712
Date Published2010///
ISBN Number0021-9258
KeywordsKalanchoe oxidosqualene cyclase triterpenoid sequence
Abstract

The first committed step in triterpenoid biosynthesis is the cyclization of oxidosqualene to polycyclic alcs. or ketones C30H50O. It is catalyzed by single oxidosqualene cyclase (OSC) enzymes that can carry out varying nos. of carbocation rearrangements and, thus, generate triterpenoids with diverse carbon skeletons. OSCs from diverse plant species have been cloned and characterized, the large majority of them catalyzing relatively few rearrangement steps. It was recently predicted that special OSCs must exist that can form friedelin, the pentacyclic triterpenoid whose formation involves the max. possible no. of rearrangement steps. The goal of the present study, therefore, was to clone a friedelin synthase from Kalanchoe daigremontiana, a plant species known to accumulate this triterpenoid in its leaf surface waxes. Five OSC cDNAs were isolated, encoding proteins with 761-779 amino acids and sharing between 57.4 and 94.3% nucleotide sequence identity. Heterologous expression in yeast and GC-MS analyses showed that one of the OSCs generated the steroid cycloartenol together with minor side products, whereas the other four enzymes produced mixts. of pentacyclic triterpenoids dominated by lupeol (93%), taraxerol (60%), glutinol (66%), and friedelin (71%), resp. The cycloartenol synthase was found expressed in all leaf tissues, whereas the lupeol, taraxerol, glutinol, and friedelin synthases were expressed only in the epidermis layers lining the upper and lower surfaces of the leaf blade. It is concluded that the function of these enzymes is to form resp. triterpenoid aglycons destined to coat the leaf exterior, probably as defense compds. against pathogens or herbivores. [on SciFinder(R)]