Isoprenoid biosynthesis: The evolution of two ancient …

N2 - The core membrane lipids in archaebacteria are isoprenoid ether derivatives of glycerol instead of fatty acid esters found in other organisms. Activities for three key enzymes in membrane lipid biosynthesis, isopentenyl diphosphate (IPP) isomerase, geranylgeranyl diphosphate (GGPP) synthase, and 3-O-geranylgeranylglyceryl phosphate (GGGP) synthase were found in the cytosolic fractions of cell-free homogenates from the strict anaerobe Methanobacterium thermoautotrophicum and the extreme halophile Halobacterium halobium. The substrate selectivities of GGGP synthase from both sources were similar and indicate a common pathway for biosynthesis of the isoprenoid compounds in core membrane lipids from methanogenic and halophilic archaebacteria.

 Biosynthesis of polyisoprenoid alcohols and their biologicalrole have been reviewed in 2005 ().

N2 - The carbon skeletons of over 55,000 naturally occurring isoprenoid compounds are constructed from four fundamental coupling reactions: chain elongation, cyclopropanation, branching, and cyclobutanation. Enzymes that catalyze chain elongation and cyclopropanation are well studied, whereas those that catalyze branching and cyclobutanation are unknown. We have catalyzed the four reactions with chimeric proteins generated by replacing segments of a chain-elongation enzyme with corresponding sequences from a cyclopropanation enzyme. Stereochemical and mechanistic considerations suggest that the four coupling enzymes could have evolved from a common ancestor through relatively small changes in the catalytic site.


Isoprenoid Compounds - CliffsNotes Study Guides

T1 - Chimeras of two isoprenoid synthases catalyze all four coupling reactions in isoprenoid biosynthesis

AB - The carbon skeletons of over 55,000 naturally occurring isoprenoid compounds are constructed from four fundamental coupling reactions: chain elongation, cyclopropanation, branching, and cyclobutanation. Enzymes that catalyze chain elongation and cyclopropanation are well studied, whereas those that catalyze branching and cyclobutanation are unknown. We have catalyzed the four reactions with chimeric proteins generated by replacing segments of a chain-elongation enzyme with corresponding sequences from a cyclopropanation enzyme. Stereochemical and mechanistic considerations suggest that the four coupling enzymes could have evolved from a common ancestor through relatively small changes in the catalytic site.