Inhibition studies of serine hydrolases by cyclic phosphates and phosphonates

The serine hydrolase superfamily is one of the largest known enzyme families comprising approximately 1% of the predicted protein product in human genome. This family of enzymes contains a catalytic triad that is mainly consists of serine, aspartic acid/glutamic acid and histidine residues in their active sites. It has been proposed that the potential drug targets for Alzheimer's disease and diabetes type 2 are enzymes that belong to this enzyme family.;Acetylcholinesterase (AChE) is an enzyme that catalyzes the breakdown of acetylcholine, a neurotransmitter that helps transport information from one nerve cell to another. Breakdown of acetylcholine in Alzheimer's disease patients enhances memory loss, which could be reduced if AChE is inhibited. Cyclophostin, a bicyclic phosphate, is a natural product inhibitor of AChE having an IC50 of 8 e-4 muM. The laboratory-synthesized mono- and bicyclic analogs of phosphonate analog of cyclophostin exhibited low muM potency against human AChE. It is established that these analogs covalently modify the active site of AChE and do not dissociate from the active site upon treatment with oximes. From a comparative analysis of kinetic data these compounds are less toxic and milder than the existing AChE inhibitors and can be used as potential chemotherapeutic agent against Alzheimer's disease.;Hormone-sensitive lipase (HSL) is another serine hydrolase enzyme that hydrolyzes lipids in the form of triglycerides. It is a homodimer of 84 kDa subunits and is mostly found in adipose tissues. HSL is a potential drug target for diabetes type 2. The activity of HSL must be inhibited in insulin deficient patients to lower the risk of associated cardiovascular disease. Cyclipostin is a natural product inhibitor of HSL. Laboratory-synthesized monocyclic phosphonate analogs of cyclipostin having varying C-chain length exhibited muM potency against rat HSL. The potency of these analogs improved upon introducing longer C-chain like C16. This class of compounds showed an aggregation property that affected their potency against the enzyme. The attachment of the C-chain at the P-center of the monocyclic phosphonate analog considerably improved the potency (almost 10 fold).;HSL has not been crystallized yet, so the biophysical events triggering the translocation of the enzyme towards lipid storage modules upon phosphorylation are not well established. It is shown that the translocation of the enzyme happens due to the hydrophobic surface exposure of the protein upon phosphorylation. It is revealed from fluorescence data that at least S563 and S565 phosphorylation sites do not have a significant effect on the exposure process. In vivo translocation experiments revealed that for translocation, the beta-adrenergic hormone (forskolin) treatment is important for the co-localization of protein to the lipid.