143678-64-2Relevant academic research and scientific papers
Application of Bronsted-type LFER in the study of the phospholipase C mechanism
Mihai, Cornelia,Kravchuk, Alexander V.,Tsai, Ming-Daw,Bruzik, Karol S.
, p. 3236 - 3242 (2007/10/03)
Phosphatidylinositol-specific phospholipase C cleaves the phosphodiester bond of phosphatidylinositol to form inositol 1,2-cyclic phosphate and diacylglycerol. This enzyme also accepts a variety of alkyl and aryl inositol phosphates as substrates, making it a suitable model enzyme for studying mechanism of phosphoryl transfer by probing the linear free-energy relationship (LFER). In this work, we conducted a study of Bronsted-type relationship (log k = βlg pKa + C) to compare mechanisms of enzymatic and nonenzymatic reactions, confirm the earlier proposed mechanism, and assess further the role of hydrophobicity in the leaving group as a general acid-enabling factor. The observation of the high negative Bronsted coefficients for both nonenzymatic (βlg = -0.65 to -0.73) and enzymatic cleavage of aryl and nonhydrophobic alkyl inositol phosphates (βlg = -0.58) indicates that these reactions involve only weak general acid catalysis. In contrast, the enzymatic cleavage of hydrophobic alkyl inositol phosphates showed low negative Bronsted coefficient (βlg = -0.12), indicating a small amount of the negative charge on the leaving group and efficient general acid catalysis. Overall, our results firmly support the previously postulated mechanism where hydrophobic interactions between the enzyme and remote parts of the leaving group induce an unprecedented negative-charge stabilization on the leaving group in the transition state.
Synthesis and Kinetic Evaluation of Inhibitors of the Phosphatidylinositol-Specific Phospholipase C from Bacillus cereus
Matrin, Stephen F.,Wagman, Allan S.
, p. 8016 - 8023 (2007/10/03)
Substrate analogues of phosphatidylinositol (1) were synthesized and evaluated as potential inhibitors of the bacterial phosphatidylinositol-specific phospholipase C (PI-PLC) from Bacillus cereus.The chiral analogues of the water-soluble phospholipid substrate 5 were designed to probe the effects of varying the inositol C-2 hydroxyl group, which generally believed to serve as the nucleophile in the first step of the hydrolysis of phosphatidylinositols by PI-PLC.In the analogues 6-9, the C-2 hydroxyl group on the inositol ring of the phosphatidylinositol derivatives was rationally altered in several ways.Inversion of the stereochemistry at C-2 of the inositol ring led to the scyllo derivative 6.The inositol C-2 hydroxy group was replaced with inversion by a fluorine to produce the scyllo-fluoro inositol 7 and with a hydrogen atom to furnish the 2-deoxy compound 8.The C-2 hydroxyl group was O-methylated to prepare the methoxy derivative 9.The natural inositol configuration at C-2 was retained in the nonhydrolyzable phosphorodithioate analogue 10.The inhibition of PI-PLC by each of these analogues was then analyzed in a continuous assay using D-myo-inositol 1-(4-nitrophenyl phosphate) (25) as a chromogenic substrate.The kinetic parameters for each of these phosphatidylinositol derivatives were determined, and each was found to be a competitive inhibitor with Ki's as follows: 6, 0.2 mM; 10, 0.6 mM; 8, 2.6 mM; 9, 6.6 mM; and 7, 8.8 mM.This study further establishes that the hydrolysis of phosphatidylinositol analogues by bacterial PI-PLC requires not only the presence of a C-2 hydroxyl group on the inositol ring, but the stereochemistry at this position must also correspond to the natural myo-configuration.For future inhibitor design, it is perhaps noteworthy that the best inhibitors 6 and 10 each possess a hydroxyl group at the 2-position.Several of the inhibitors identified in this study are now being used to obtain crystallographic information for an enzyme-inhibitor complex to gain further insights regarding the mechanism of hydrolysis of phosphatidylinositides by this PI-PLC.
