(S)-Geranylgeranylglyceryl Phosphate Synthase

The first pathway-specific step in the biosynthesis of the core membrane diether lipids in archaebacteria is the alkylation of the primary hydroxyl group in (S).glyc. eryl phosphate by geranylgeranyl diphosphate. The reaction is catalyzed by (S)-3-0·geranylgeranylglyceryl phosphate «S)-GGGP) synthase. The cytosolic enzyme was purified to homogeneity from the moderately thermophilic archae bacterium Methanobacterium thermoautotrophicum by a combination of ammonium sulfate precipitation, four chromatographic steps (DE52, Q-Sepharose, phenyl.Superose, and Protein Pak), and native polyacrylamide gel electrophoresis. SDS-polyacrylamide gel electrophoresis of gel-purified GGGP synthase gave a single band at 29 kDa. The enzyme requires Mg2+ for optimal activity, although prenyltransfer is also seen in buffers containing Mn2 + or Zn2 +. A well defined pH optimum occurs between 6.0 and 7.5. Maximal activity is seen at 50-65 ·C. The Michaelis constants for GGGP synthase are V max = 4.1 :t 0.5 JImol minmg-t, K??PP = 4.1 :t 1.1 JIM, and Kfl = 41 :t 5 JIM.