The Experts below are selected from a list of 4974 Experts worldwide ranked by ideXlab platform
Michael J Krische - One of the best experts on this subject based on the ideXlab platform.
-
enantioselective carbonyl allylation crotylation and tert Prenylation of furan methanols and furfurals via iridium catalyzed transfer hydrogenation
ChemInform, 2010Co-Authors: Benjamin Bechem, Ryan L Patman, Stephen A K Hashmi, Michael J KrischeAbstract:5-Substituted-2-furan methanols 1a-c are subject to enantioselective carbonyl allylation, crotylation and tert-Prenylation upon exposure to allyl acetate, alpha-methyl allyl acetate, or 1,1-dimethylallene in the presence of an ortho-cyclometalated iridium catalyst modified by (R)-Cl,MeO-BIPHEP, (R)-C3-TUNEPHOS, and (R)-C3-SEGPHOS, respectively. In the presence of 2-propanol, but under otherwise identical conditions, the corresponding substituted furfurals 2a-c are converted to identical products of allylation, crotylation, and tert-Prenylation. Optically enriched products of carbonyl allylation, crotylation, and reverse Prenylation 3b, 4b, and 5b were subjected to Achmatowicz rearrangement to furnish the corresponding gamma-hydroxy-beta-pyrones 6a-c, respectively, with negligible erosion of enantiomeric excess.
-
enantioselective iridium catalyzed carbonyl allylation from the alcohol oxidation level via transfer hydrogenation minimizing pre activation for synthetic efficiency
Chemical Communications, 2009Co-Authors: Michael J KrischeAbstract:Existing methods for enantioselective carbonyl allylation, crotylation and tert-Prenylation require stoichiometric generation of pre-metallated nucleophiles, and often employ stoichiometric chiral modifiers. Under the conditions of transfer hydrogenation employing an ortho-cyclometallated iridium C,O-benzoate catalyst, enantioselective carbonyl allylations, crotylations and tert-Prenylations are achieved in the absence of stoichiometric metallic reagents or stoichiometric chiral modifiers. Moreover, under transfer hydrogenation conditions, primary alcohols function dually as hydrogen donors and aldehyde precursors, enabling enantioselective carbonyl addition directly from the alcohol oxidation level.
Kirill Alexandrov - One of the best experts on this subject based on the ideXlab platform.
-
design and application of in vivo fret biosensors to identify protein Prenylation and nanoclustering inhibitors
Chemistry & Biology, 2012Co-Authors: Monika Kohnke, Kirill Alexandrov, Steven Schmitt, Nicholas Ariotti, Andrew M Piggott, Robert G Parton, Ernest Lacey, Robert J Capon, Daniel AbankwaAbstract:Protein Prenylation is required for membrane anchorage of small GTPases. Correct membrane targeting is essential for their biological activity. Signal output of the prenylated proto-oncogene Ras in addition critically depends on its organization into nanoscale proteolipid assemblies of the plasma membrane, so called nanoclusters. While protein Prenylation is an established drug target, only a handful of nanoclustering inhibitors are known, partially due to the lack of appropriate assays to screen for such compounds. Here, we describe three cell-based high-throughput screening amenable Forster resonance energy transfer NANOclustering and Prenylation Sensors (NANOPS) that are specific for Ras, Rho, and Rab proteins. Rab-NANOPS provides the first evidence for nanoclustering of Rab proteins. Using NANOPS in a cell-based chemical screen, we now identify macrotetrolides, known ionophoric antibiotics, as submicromolar disruptors of Ras nanoclustering and MAPK signaling.
-
a protein fluorescence amplifier continuous fluorometric assay for rab geranylgeranyltransferase
ChemBioChem, 2006Co-Authors: Herbert Waldmann, Roger S. Goody, Reinhard Reents, Frank H Ebetino, Kirill AlexandrovAbstract:A 23-fold enhancement of fluorescence is observed upon RabGGTase-mediated protein Prenylation by NBD-FPP. We propose that the chaperone of prenylated Rab GTPases, REP, which harbors the conjugated prenyl moieties, functions as a fluorescence amplifier and leads to intermolecular fluorescence enhancement. This reaction was characterized and used to develop a fluorescent Prenylation assay that can be adapted for a high-throughput format.
-
Phosphoisoprenoids modulate association of Rab geranylgeranyltransferase with REP-1.
The Journal of biological chemistry, 2001Co-Authors: Nicolas H Thoma, Roger S. Goody, Andrei Iakovenko, Kirill AlexandrovAbstract:Abstract Rab geranylgeranyltransferase (RabGGTase or GGTase-II) catalyzes the post-translational Prenylation of Rab proteins. Rab proteins are recognized as substrates only when they are complexed to Rab Escort Protein (REP). The classical model of Prenylation complex assembly assumes initial formation of the Rab·REP binary complex, which subsequently binds to RabGGTase loaded with the isoprenoid donor geranylgeranyl pyrophosphate (GGpp). We demonstrate here that REP-1 can also associate with RabGGTase in the absence of Rab protein and that this interaction is dramatically strengthened by the presence of phosphoisoprenoids such as GGpp. The GGpp-dependent interaction between RabGGTase and REP-1 was observed using affinity precipitations and gel filtration and was quantitated on the basis of fluorescence assays. In the presence of GGpp, REP-1 binds to RabGGTase with a K dvalue of ∼10 nm, while in its absence the affinity between the two proteins is in the micromolar range. We further demonstrate that binding of Rab7 to the RabGGTase·GGpp·REP-1 complex occurs without prior dissociation of REP-1. Analysis of binding and Prenylation rate constants indicate that the RabGGTase·GGpp·REP-1 complex can function as a kinetically competent intermediate of the Prenylation reaction. We conclude that, depending on the prevailing concentrations, binding of REP-1 to RabGGTase in the presence of GGpp may serve as an alternative pathway for the assembly of the Prenylation machinery in vivo. Implications of these findings for the role of REP-1 in the Prenylation reaction are discussed.
J B Gibbs - One of the best experts on this subject based on the ideXlab platform.
-
protein Prenylation in eukaryotic microorganisms genetics biology and biochemistry
Molecular Microbiology, 1994Co-Authors: C A Omer, J B GibbsAbstract:Summary Modrfication of proteins at C-terminal cysteine residue(s) by the isoprenoids farnesyl (C15) and geranylgeranyl (C20) is essential for the biological function of a number of eukaryotic proteins including fungal mating factors and the small, GTP-binding proteins of the Ras superfamily. Three distinct enzymes, conserved between yeast and mammals, have been identified that prenylate proteins: farnesyl protein transferase, geranylgeranyl protein transferase type I and geranylgeranyl protein transferase type II. Each prenyl protein transferase has its own protein substrate specificity. Much has been learned about the biology, genetics and biochemistry of protein Prenylation and prenyl protein transferases through studies of eukaryotic microorganisms, particularly Saccharo-myces cerevisiae. The functional Importance of protein Prenylation was first demonstrated with fungal mating factors. The initial genetic analysis of prenyl protein transferases was in S. cerewisiae with the isolation and subsequent characterization of mutations in the RAM1, RAM2, CDC43 and BET2 genes, each of which encodes a prenyl protein transferase subunit. We review here these and other studies on protein Prenylation in eukaryotic microbes and how they relate to and have contributed to our knowledge about protein Prenylation in all eukaryotic cells.
Carol A. Fierke - One of the best experts on this subject based on the ideXlab platform.
-
SmgGDS-607 Regulation of RhoA GTPase Prenylation Is Nucleotide-Dependent
2018Co-Authors: Benjamin C. Jennings, Alexis J. Lawton, Zeinab Rizk, Carol A. FierkeAbstract:Protein Prenylation involves the attachment of a hydrophobic isoprenoid moiety to the C-terminus of proteins. Several small GTPases, including members of the Ras and Rho subfamilies, require Prenylation for their normal and pathological functions. Recent work has suggested that SmgGDS proteins regulate the Prenylation of small GTPases in vivo. Using RhoA as a representative small GTPase, we directly test this hypothesis using biochemical assays and present a mechanism describing the mode of Prenylation regulation. SmgGDS-607 completely inhibits RhoA Prenylation catalyzed by protein geranylgeranyltransferase I (GGTase-I) in an in vitro radiolabel incorporation assay. SmgGDS-607 inhibits Prenylation by binding to and blocking access to the C-terminal tail of the small GTPase (substrate sequestration mechanism) rather than via inhibition of the prenyltransferase activity. The reactivity of GGTase-I with RhoA is unaffected by addition of nucleotides. In contrast, the affinity of SmgGDS-607 for RhoA varies with the nucleotide bound to RhoA; SmgGDS-607 has a higher affinity for RhoA-GDP compared to RhoA-GTP. Consequently, the Prenylation blocking function of SmgGDS-607 is regulated by the bound nucleotide. This work provides mechanistic insight into a novel pathway for the regulation of small GTPase protein Prenylation by SmgGDS-607 and demonstrates that peptides are a good mimic for full-length proteins when measuring GGTase-I activity
-
Analogs of farnesyl diphosphate alter CaaX substrate specificity and reactions rates of protein farnesyltransferase.
Bioorganic & medicinal chemistry letters, 2015Co-Authors: Benjamin C. Jennings, Yen Chih Wang, Mark D Distefano, Richard A. Gibbs, Amy M. Danowitz, Carol A. FierkeAbstract:Attempts to identify the prenyl-proteome of cells or changes in Prenylation following drug treatment have used 'clickable' alkyne-modified analogs of the lipid substrates farnesyl- and geranylgeranyl-diphosphate (FPP and GGPP). We characterized the reactivity of four alkyne-containing analogs of FPP with purified protein farnesyltransferase and a small library of dansylated peptides using an in vitro continuous spectrofluorimetric assay. These analogs alter Prenylation specificity and reactivity suggesting that in vivo results obtained using these FPP analogs should be interpreted cautiously.
-
Expansion of Protein Farnesyltransferase Specificity Using “Tunable” Active Site Interactions DEVELOPMENT OF BIOENGINEERED Prenylation PATHWAYS
The Journal of biological chemistry, 2012Co-Authors: James L. Hougland, Soumyashree A. Gangopadhyay, Carol A. FierkeAbstract:Post-translational modifications play essential roles in regulating protein structure and function. Protein farnesyltransferase (FTase) catalyzes the biologically relevant lipidation of up to several hundred cellular proteins. Site-directed mutagenesis of FTase coupled with peptide selectivity measurements demonstrates that molecular recognition is determined by a combination of multiple interactions. Targeted randomization of these interactions yields FTase variants with altered and, in some cases, bio-orthogonal selectivity. We demonstrate that FTase specificity can be "tuned" using a small number of active site contacts that play essential roles in discriminating against non-substrates in the wild-type enzyme. This tunable selectivity extends in vivo, with FTase variants enabling the creation of bioengineered parallel Prenylation pathways with altered substrate selectivity within a cell. Engineered FTase variants provide a novel avenue for probing both the selectivity of Prenylation pathway enzymes and the effects of Prenylation pathway modifications on the cellular function of a protein.
-
Getting a handle on protein Prenylation
Nature Chemical Biology, 2009Co-Authors: James L. Hougland, Carol A. FierkeAbstract:Protein Prenylation plays a key role in the localization and function of many proteins, but the number and identities of prenylated proteins are unknown. A new study uses a multidisciplinary approach to provide a broad yet detailed snapshot of Prenylation within the mammalian proteome.
Robert B Lobell - One of the best experts on this subject based on the ideXlab platform.
-
preclinical and clinical pharmacodynamic assessment of l 778 123 a dual inhibitor of farnesyl protein transferase and geranylgeranyl protein transferase type i
Molecular Cancer Therapeutics, 2002Co-Authors: Robert B Lobell, Dongming Liu, Carolyn A Buser, Joseph P Davide, Elizabeth Depuy, Kelly Hamilton, Kenneth S Koblan, Yih Lee, Scott D Mosser, Sherri L MotzelAbstract:Farnesyl:protein transferase (FPTase) inhibitors were developed as anti-Ras drugs, but they fail to inhibit Ki-Ras activity because Ki-Ras can be modified by geranylgeranyl:protein transferase type-I (GGPTase-I). L-778,123, an inhibitor of FPTase and GGPTase-I, was developed in part because it can completely inhibit Ki-Ras Prenylation. To support the clinical development of L-778,123, we developed pharmacodynamic assays using peripheral blood mononuclear cells (PBMCs) to measure the inhibition of Prenylation of HDJ2 and Rap1A, proteins that are FPTase- and GGPTase-I substrates, respectively. We validated these assays in animal models and show that inhibition of HDJ2 Prenylation in mouse PBMCs correlates with the concentration of FPTase inhibitors in blood. In dogs, continuous infusion of L-778,123 inhibited both HDJ2 and Rap1A Prenylation in PBMCs, but we did not detect inhibition of Ki-Ras Prenylation. We reported previously results from the first L-778,123 Phase I trial that showed a dose-dependent inhibition of HDJ2 farnesylation in PBMCs. In this report, we present additional analysis of patient samples from this trial and a second Phase I trial of L-778,123, and demonstrate the inhibition of both HDJ2 and Rap1A Prenylation in PBMC samples. This study represents the first demonstration of GGPTase-I inhibition in humans. However, no inhibition of Ki-Ras Prenylation by L-778,123 was detected in patient samples. These results confirm the pharmacologic profile of L-778,123 in humans as a dual inhibitor of FPTase and GGPTase-I, but indicate that the intended target of the drug, Ki-Ras, was not inhibited.
-
evaluation of farnesyl protein transferase and geranylgeranyl protein transferase inhibitor combinations in preclinical models
Cancer Research, 2001Co-Authors: Robert B Lobell, Carolyn A Buser, Joseph P Davide, Charles A Omer, Marc Abrams, Hema Bhimnathwala, Mary Jo Brucker, Jane S Desolms, Christopher J Dinsmore, Michelle EllishutchingsAbstract:Farnesyl:protein transferase (FPTase) inhibitors (FTIs) were originally developed as potential anticancer agents targeting the ras oncogene and are currently in clinical trials. Whereas FTIs inhibit the farnesylation of Ha-Ras, they do not completely inhibit the Prenylation of Ki-Ras, the allele most frequently mutated in human cancers. Whereas farnesylation of Ki-Ras is blocked by FTIs, Ki-Ras remains prenylated in FTI-treated cells because of its modification by the related prenyltransferase, geranylgeranyl:protein transferase type I (GGPTase-I). Hence, cells transformed with Ki-ras tend to be more resistant to FTIs than Ha-ras-transformed cells. To determine whether Ki-ras-transformed cells can be targeted by combining an FTI with a GGPTase-I inhibitor (GGTI), we evaluated potent, selective FTIs, GGTIs, and dual Prenylation inhibitors (DPIs) that have both FTI and GGTI activity. We find that in human PSN-1 pancreatic tumor cells, which harbor oncogenic Ki-ras, and in other tumor lines having either wild-type or oncogenic Ki-ras, treatment with an FTI/GGTI combination or with a DPI blocks Ki-Ras Prenylation and induces markedly higher levels of apoptosis relative to FTI or GGTI alone. We demonstrate that these compounds can inhibit their enzyme targets in mice by monitoring pancreatic and tumor tissues from treated animals for inhibition of Prenylation of Ki-Ras, HDJ2, a substrate specific for FPTase, and Rap1A, a substrate specific for GGPTase-I. Continuous infusion (72 h) of varying doses of GGTI in conjunction with a high, fixed dose of FTI causes a dose-dependent inhibition of Ki-Ras Prenylation. However, a 72-h infusion of a GGTI, at a dose sufficient to inhibit Ki-Ras Prenylation in the presence of an FTI, causes death within 2 weeks of the infusion when administered either as monotherapy or in combination with an FTI. DPIs are also lethal after a 72-h infusion at doses that inhibit Ki-Ras Prenylation. Because 24 h infusion of a high dose of DPI is tolerated and inhibits Ki-Ras Prenylation, we compared the antitumor efficacy from a 24-h FTI infusion to that of a DPI in a nude mouse/PSN-1 tumor cell xenograft model and in Ki-ras transgenic mice with mammary tumors. The FTI and DPI were dosed at a level that provided comparable inhibition of FPTase. The FTI and the DPI displayed comparable efficacy, causing a decrease in growth rate of the PSN-1 xenograft tumors and tumor regression in the transgenic model, but neither treatment regimen induced a statistically significant increase in tumor cell apoptosis. Although FTI/GGTI combinations elicit a greater apoptotic response than either agent alone in vitro, the toxicity associated with GGTI treatment in vivo limits the duration of treatment and, thus, may limit the therapeutic benefit that might be gained by inhibiting oncogenic Ki-Ras through dual prenyltransferase inhibitor therapy.
