guanosine-diphosphate and 4-4-difluoro-4-bora-3a-4a-diaza-s-indacene

A microfluidic chip consisting of parallel channels designed for rapid electrophoretic enzyme assays was developed. Radial arrangement of channels and a common waste channel allowed chips with 16 and 36 electrophoresis units to be fabricated on a 7.62 x 7.62 cm(2) glass substrate. Fluorescence detection was achieved using a Xe arc lamp source and commercial charge-coupled device (CCD) camera to image migrating analyte zones in individual channels. Chip performance was evaluated by performing electrophoretic assays for G protein GTPase activity on chip using BODIPY-GTP as enzyme substrate. A 16-channel design proved to be useful in extracting kinetic information by allowing serial electrophoretic assays from 16 different enzyme reaction mixtures at 20 s intervals in parallel. This system was used to rapidly determine enzyme concentrations, optimal enzymatic reaction conditions, and Michaelis-Menten constants. A chip with 36 channels was used for screening for modulators of the G protein-RGS protein interaction by assaying the amount of product formed in enzyme reaction mixtures that contained test compounds. Thirty-six electrophoretic assays were performed in 30 s suggesting the potential throughput up to 4320 assays/h with appropriate sample handling procedures. Both designs showed excellent reproducibility of peak migration time and peak area. Relative standard deviations of normalized peak area of enzymatic product BODIPY-GDP were 5% and 11%, respectively, in the 16- and 36-channel designs.

Topics: Boron Compounds; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Electrophoresis, Capillary; GTP Phosphohydrolases; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; Guanosine Triphosphate; Hydrolysis; Kinetics; Microfluidic Analytical Techniques; RGS Proteins; Rhodamines

Epidermal-type Transglutaminase 3 (TGase 3) is a Ca(2+)-dependent enzyme involved in the cross-linking of structural proteins required in the assembly of the cell envelope. We have recently shown that calcium-activated TGase 3, like TGase 2, can bind, hydrolyze, and is inhibited by GTP despite lacking structural homology with other GTP-binding proteins. Here we report the crystal structure determined at 2.0 A resolution of TGase 3 in complex with GMP to elucidate the structural features required for nucleotide recognition. Binding affinities for various nucleotides were found by fluorescence displacement to be as follows: guanosine 5'-3-O-(thio)triphosphate (GTPgammaS) (0.4 microm), GTP (0.6 microm), GDP (1.0 microm), GMP (0.4 microm), and ATP (28.0 microm). Furthermore, we found that GMP binds as a reversible, noncompetitive inhibitor of TGase 3 transamidation activity, similar to GTPgammaS and GDP. A genetic algorithm similarity program (GASP) approach (virtual ligand screening) identified three compounds from the Lead Quest trade mark data base (Tripos Inc.) based on superimposition of GTPgammaS, GDP, and GMP guanine nucleotides from our crystal structures to generate the minimum align flexible fragment. These three were nucleotide analogs without a phosphate group containing the minimal binding motif for TGase 3 that includes a nucleoside recognition groove. Binding affinities were measured as follows: TP349915 (K(d) = 4.1 microm), TP395289 (K(d) = 38.5 microm), TP394305 (K(d) = 1.0 mm). Remarkably, these compounds do not inhibit but instead activate TGase 3 transamidation by about 10-fold. These results suggest that the nucleotide binding pocket in TGase 3 may be exploited to either enhance or inhibit the enzymatic activity as required for different therapeutic approaches.

Topics: Adenosine Triphosphate; Algorithms; Boron Compounds; Cell Membrane; Crystallography, X-Ray; Dose-Response Relationship, Drug; Electrons; Guanine; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; Guanosine Monophosphate; Guanosine Triphosphate; Humans; Hydrolysis; Kinetics; Ligands; Models, Chemical; Models, Molecular; Phosphates; Protein Binding; Protein Conformation; Spectrometry, Fluorescence

Topics: Boron Compounds; Fluorescent Dyes; GTP Phosphohydrolases; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; Heterotrimeric GTP-Binding Proteins; Kinetics; Protein Subunits; Spectrometry, Fluorescence

Three BODIPY GTPgammaS analogs (FL, 515, and TR), BODIPY FL GppNHp and BODIPY FL GTP molecules were synthesized as possible fluorescent probes to study guanine nucleotide binding spectroscopically. Binding to G(alphao) increases baseline analog fluorescence by 6-, 8.5-, 2.8-, 3.5-, and 3.0-fold, respectively. Binding of GTPgammaS and GppNHp analogs to G(alphao) is of high affinity (K(D) 11, 17, 55, and 110 nM, respectively) and reaches a stable plateau while fluorescence of BODIPY FL GTP shows a transient increase which returns to baseline. Furthermore, BODIPY FL GTPgammaS shows varying affinities for alpha(o), alpha(s), alpha(i1), and alpha(i2) (6, 58, 150, and 300 nM). The affinities of BODIPY FL GppNHp for all four G(alpha) subunits are 10-fold lower than for BODIPY FL GTPgammaS. Half-times for the fluorescence increase are consistent with known GDP release rates for those proteins. Enhancement of fluorescence upon binding the G(alpha) subunit is most likely due to a rotation around the gamma-thiol (GTPgammaS) or the 3' ribose-hydroxyl (GppNHp) bond to relieve the quenching of BODIPY fluorescence by the guanine base. Binding to G(alpha) exposes the BODIPY moiety to the external environment, as seen by an increase in sodium iodide quenching. The visible excitation and emission spectra and high fluorescence levels of these probes permit robust real-time detection of nucleotide binding.

Topics: Boron Compounds; Escherichia coli; Fluorescent Dyes; GTP-Binding Proteins; Guanosine Diphosphate; Guanosine Triphosphate; Protein Binding; RGS Proteins

In mast cells, activation of GTP-binding proteins induces centripetal reorganization of actin filaments. This effect is due to disassembly, relocalization, and polymerization of F-actin and is dependent on two small GTPases, Rac and Rho. Activities of Rac and Rho are also essential for the secretory function of mast cells. In response to GTP-gamma-S and/or calcium, only a proportion of permeabilized mast cells is capable of secretory response. Here, we have compared actin organization of secreting and nonsecreting cell populations. We show that the cytoskeletal and secretory responses are strongly correlated, indicating a common upstream regulator of the two functions. The secreting cell population preferentially displays both relocalization and polymerization of actin. However, when actin relocalization or polymerization is inhibited by phalloidin or cytochalasin, respectively, secretion is unaffected. Moreover, the ability of the constitutively active mutants of Rac and Rho to enhance secretion is also unaffected in the presence of cytochalasin. Therefore, Rac and Rho control these two functions by divergent, parallel signaling pathways. Cortical actin disassembly occurs in both secreting and nonsecreting populations and does not, by itself, induce exocytosis. A model for the control of exocytosis is proposed that includes at least four GTP-binding proteins and suggests the presence of both shared and divergent signaling pathways from Rac and Rho.

Topics: Actins; Animals; beta-N-Acetylhexosaminidases; Boron Compounds; Cell Membrane Permeability; Cells, Cultured; Concanavalin A; Cytochalasins; Cytoskeleton; Exocytosis; Flow Cytometry; Fluorescein-5-isothiocyanate; GTP-Binding Proteins; GTPase-Activating Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; Mast Cells; Microscopy, Confocal; Proteins; rac GTP-Binding Proteins; Rats; rho GTP-Binding Proteins; rhoA GTP-Binding Protein; Staining and Labeling; Thionucleotides