Synthesis and application of a fluorescent substrate analogue to study ligand interactions for undecaprenyl pyrophosphate synthase.
Farnesyl pyrophosphate (FPP) serves as a common substrate for many prenyltransferases involved in the biosynthesis of isoprenoid compounds. Undecaprenyl pyrophosphate synthase (UPPs) catalyzes the chain elongation of FPP to C(55) undecaprenyl pyrophosphate (UPP) which acts as a lipid carrier in bacterial peptidoglycan synthesis. In this study, 7-(2,6-dimethyl-8-diphospho-2,6-octadienyloxy)-8-methyl-4-trifluoromethyl-chromen-2-one geranyl pyrophosphate, a fluorescent analogue of FPP, was prepared and utilized to study ligand interactions with E. coli UPPs. This compound displays an absorbance maximum at 336 nm and emission maximum at 460 nm without interference from protein autofluorescence. It is a competitive inhibitor with respect to FPP (K(i) = 0.57 microM) and also serves as an alternative substrate (K(m) = 0.69 microM and k(cat) = 0.02 s(-)(1)), but mainly reacts with one isopentenyl pyrophosphate (IPP) probably due to unfavorable product translocation. Fluorescence intensity of this compound is reduced when bound to the enzyme (1:1 stoichiometry), and is recovered by FPP replacement. Using stopped-flow apparatus, the interaction of enzyme with the compound was measured (k(on) = 55.3 microM(-)(1) s(-)(1) and k(off) = 31.6 s(-)(1)). The product dissociation rate constant (0.5 s(-)(1)) determined from the competition experiments is consistent with our previous prediction from kinetic simulation. Unlike several other prenyltransferase reactions in which FPP dissociates slowly, UPPs binds FPP in a rapid equilibrium manner with a fast release rate constant of 30 s(-)(1). The fluorescent analogue of FPP presented here may provide a tool to investigate the ligand interactions for a broad class of FPP-binding proteins.
Chen
Annie P-C
AP
Institute of Biological Chemistry, Academia Sinica, Taipei 11529, Taiwan.
Chen
Yi-Hung
YH
Liu
Hsiao-Pei
HP
Li
Yu-Chin
YC
Chen
Chao-Tsen
CT
Liang
Po-Huang
PH
D019883:Alkyl and Aryl Transferases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D004926:Escherichia coli / Q000201:enzymology; D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D020128:Inhibitory Concentration 50; D007700:Kinetics; D008024:Ligands; D011106:Polyisoprenyl Phosphates / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D012717:Sesquiterpenes; D013050:Spectrometry, Fluorescence
C471862:7-(2,6-dimethyl-8-diphospho-2,6-octadienyloxy)-8-methyl-4-trifluoromethylchromen-2-one; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D008024:Ligands; D011106:Polyisoprenyl Phosphates; D012717:Sesquiterpenes; C004808:farnesyl pyrophosphate; D019883:Alkyl and Aryl Transferases; C023266:undecaprenyl pyrophosphate synthetase