Identification and Characterization of Geranylgeraniol Kinase and Geranylgeranyl Phosphate Kinase from the Archaebacterium Sulfolobus acidocaldarius

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Geranylgeranyl diphosphate is an important precursor of archaebacterial ether-linked lipids, and it has been thought that all of this compound is “de novo” synthesized by geranylgeranyl diphosphate synthase. We studied the phosphorylation of geranylgeraniol, which seems to be related to the salvage pathway of biosynthesis of archaebacterial ether-linked lipids, in the Archaebacterium Sulfolobus acidocaldarius. Activities of geranylgeraniol kinase and geranylgeranyl phosphate kinase were detected in a cell lysate of S. acidocaldarius. The two enzymes were easily separated by ultracentrifugation. The membrane fraction and the cytosolic fraction contained geranylgeraniol kinase activity and geranylgeranyl phosphate kinase activity, respectively. Geranylgeraniol kinase, which requires divalent cation such as Mg²⁺, Co²⁺, and Mn²⁺ and NTP (ATP, GTP, CTP, UTP), catalyzes monophosphorylation of (all-E) -geranylgeraniol to produce geranylgeranyl phosphate. (all-E)-Farnesol, (all-E)-hexaprenol, and (all-E)-octaprenol were also active as substrates, though they were less effective than (all-E)-geranylgeraniol. However, neither geraniol nor (2E, 6E, 10Z, 14Z, 18Z, 22Z, 26Z, 30Z, 34Z, 38Z)-undecaprenol was active. This enzyme is extremely thermostable and its pH optimal is between 6.5 and 8.5. The Michaelis constants for (all-E)-geranylgeraniol and ATP are 27nM and 650μM, respectively.