title: Implication of HMGR in homeostasis of sequestered and de novo produced precursors of the iridoid biosynthesis in leaf beetle larvae.
abstract: Insects employ iridoids to deter predatory attacks. Larvae of some Chrysomelina species are capable to produce those cyclopentanoid monoterpenes de novo. The iridoid biosynthesis proceeds via the mevalonate pathway to geranyl diphospate (GDP) subsequently converted into 8-hydroxygeraniol-8-O-beta-D-glucoside followed by the transformation into the defensive compounds. We tested whether the glucoside, its aglycon or geraniol has an impact on the activity of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR), the key regulatory enzyme of the mevalonate pathway and also the iridoid biosynthesis. To address the inhibition site of the enzyme, initially a complete cDNA encoding full length HMGR was cloned from Phaedon cochleariae. Its catalytic portion was then heterologously expressed in Escherichia coli. Purification and characterization of the recombinant protein revealed attenuated activity in enzyme assays by 8-hydroxygeraniol whereas no effect has been observed by addition of the glucoside or geraniol. Thus, the catalytic domain is the target for the inhibitor. Homology modeling of the catalytic domain and docking experiments demonstrated binding of 8-hydroxygeraniol to the active site and indicated a competitive inhibition mechanism. Iridoid producing larvae are potentially able to sequester glucosidically bound 8-hydroxygeraniol whose cleavage of the sugar moiety results in 8-hydroxygeraniol. Therefore, HMGR may represent a regulator in maintenance of homeostasis between de novo produced and sequestered intermediates of iridoid metabolism. Furthermore, we demonstrated that HMGR activity is not only diminished in iridoid producers but most likely prevalent within the Chrysomelina subtribe and also within the insecta.
authors: Department of Biochemistry, Max Planck Institute for Chemical Ecology, Hans-Knoell-Str. 8, D-07745 Jena, Germany. aburse@ice.mpg.de
authors: Antje
authors: A
authors: Burse
authors: Sindy
authors: S
authors: Frick
authors: Axel
authors: A
authors: Schmidt
authors: Rita
authors: R
authors: Buechler
authors: Maritta
authors: M
authors: Kunert
authors: Jonathan
authors: J
authors: Gershenzon
authors: Wolfgang
authors: W
authors: Brandt
authors: Wilhelm
authors: W
authors: Boland
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020134:Catalytic Domain / Q000502:physiology; D001517:Coleoptera / Q000737:chemistry / Q000201:enzymology* / Q000378:metabolism; D004331:Drosophila melanogaster / Q000378:metabolism; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism*; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000032:analysis / Q000378:metabolism*; D039823:Iridoids / Q000378:metabolism*; D007814:Larva / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D013729:Terpenes / Q000378:metabolism*
chemical_list: C471578:8-hydroxygeraniol; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D039823:Iridoids; D013729:Terpenes; D006903:Hydroxymethylglutaryl CoA Reductases