Design, Synthesis, and Biological Evaluation of Thioglucoside Analogues of Gliflozin as Potent New Gliflozin Drugs

In this study, we have investigated the potential of two classes of thioglucoside analogues of gliflozins as antidiabetic drugs, one with substitutions of S-atoms in meta-positions (similar to C-glucoside SGLT2 inhibitors, TAGs A, B, and C) and the other with substitutions of S-atoms in ortho-positions (similar to O-glucoside SGLT2 inhibitors, TAGs D, E, F, and G). These TAGs were confirmed to show good stability against β-glucosidase and to have no acute toxicity to cultured cells. Most importantly, TAGs D, E, F, and G all showed high inhibitory activity against SGLT2 (IC50: 2.0-5.9 nM) and thus have great potential to be developed as new gliflozin drugs. Compared with the synthesis of C-glucoside gliflozins, the synthesis of TAGs is simple, efficient, and associated with low costs, high yields, and very mild reaction conditions.

[Micelle-mediated extraction for concentrating conjugated bilirubin in urine]

An extraction method based on the phase separation of aqueous micellar solutions of n-octyl-beta-D-thioglucoside (OTG) was applied to the concentrating conjugated bilirubin in urine. The analyte in sample solutions could be efficiently concentrated into a small volume of surfactant-rich phase, while hydrophilic matrix components including urinary protein, ascorbic acid, and saccharide remained in the aqueous phase. The concentrated OTG negligibly affected the diazo reaction and the subsequent spectrophotometric detection. Conjugated bilirubin was successfully determined in the concentration range from 0.05 microgram/ml to 5 micrograms/ml with a 96-well microplate reader absorption spectrophotometer.

ATP hydrolytic activity of an iron-stimulated P-type ATPase of mouse liver microsomes

Mouse liver microsomes treated with octylthioglucoside were examined for iron-stimulated ATPase activity. The activity was about 6 mumol Pi/mg protein/hr under optimal conditions [300 mM KC1, 3 mM MgSO4, 10 mM glutathione(GSH), 100 microM FeCl3, 3 mM ATP and 50 mM acetate buffer at pH 5.0]. The Km for iron was 20 microM. A reducing agent, such as GSH or dithiothreitol, was required for the activity, and removal of Fe2+ from the reaction mixture by bathophenan-throlinedisulfonate resulted in a complete loss of the iron-stimulated ATPase activity. Vanadate inhibited the iron-stimulated ATPase activity. These results suggest that microsomes from mouse liver contain the Fe(2+)-stimulated P-type ATPase.

Electron cryomicroscopy of bacteriorhodopsin vesicles: mechanism of vesicle formation

We obtained vesicles from purple membrane of Halobacterium halobium at different suspension compositions (pH, electrolytes, buffers), following the procedure of Kouyama et al. (1994) (J. Mol. Biol. 236:990-994). The vesicles contained bacteriorhodopsin (bR) and halolipid, and spontaneously formed during incubation of purple membrane suspension in the presence of detergent octylthioglucoside (OTG) if the protein:OTG ratio was 2:1 by weight. The size distribution of the vesicles was precisely determined by electron cryomicroscopy and was found to be almost independent on the incubation conditions (mean radius 17.9-19 nm). The size distribution in a given sample was close to the normal one, with a standard deviation of approximately +/- 1 nm. During dialysis for removal of the detergent, the vesicles diminished their radius by 2-2.5 nm. The results allow us to conclude that the driving force for the formation of bR vesicles is the preferential incorporation of OTG molecules in the cytoplasmic side of the membrane (with possible preferential delipidation of the extracellular side), which creates spontaneous curvature of the purple membrane. From the size distribution of the vesicles, we calculated the elasticity bending constant, K(B) approximately 9 x 10(-20) J, of the vesicle wall. The results provide some insight into the possible formation mechanisms of spherical assembles in living organisms. The conditions for vesicle formation and the mechanical properties of the vesicles could also be of interest with respect to the potential technological application of the bR vesicles as light energy converters.

Dermacentor andersoni: salivary gland proteins suppressing T-lymphocyte responses to concanavalin A in vitro

Salivary glands obtained from feeding adult female Dermacentor andersoni (Acari:Ixodidae) were fractionated using differential centrifugation, detergents, centrifugal concentrators incorporating filter membranes with various molecular weight cutoffs, and preparative SDS-PAGE. A lymphocyte proliferation assay was used to evaluate the effects of salivary gland fractions on ConA-induced blastogenesis of normal murine splenocytes. Lipid, soluble, and detergent-soluble fractions were found to significantly suppress ConA-induced proliferation of splenocytes. Fractions containing soluble proteins suppressed splenocyte proliferation by ca. 26%. Suppressant activity in these fractions was due to components with molecular weights greater than 30 kDa. This suppression of splenocyte proliferation occurred with as little as 0.25 microgram protein per well. Salivary gland preparative SDS-PAGE fractions containing one or more soluble polypeptides or proteins with molecular weights in the range 36 to 43 kDa significantly suppressed murine splenocyte responses to ConA in vitro.

Functional reconstitution of the Trypanosoma brucei plasma-membrane D-glucose transporter

The D-glucose transporter of Trypanosoma brucei was solubilized from the plasma membrane and reconstituted into proteoliposomes. Using the reconstitution of D-glucose transport as the assay and non-specific L-glucose uptake as control, we have purified a membrane protein fraction from T. brucei bloodstream-form ghosts by EDTA/alkali treatment and solubilization with the detergents octylglucoside or octylthioglucoside. Upon removal of the detergent by dialysis, the solubilized protein fraction was reconstituted in sonicated liposomes by a freeze/thaw-sonication step. The reconstituted transporter catalyzed specific D-glucose uptake and was compared in several characteristics with the native facilitated-diffusion transporter as present in live trypanosomes [Seyfang, A. & Duszenko, M. (1991) Eur. J. Biochem. 202, 191-196]. As in vivo, the uptake is time dependent and Na+ independent. Transporter substrate affinity and inhibitor specificity are completely retained and it is inhibited by mercuric ions, phloretin and cytochalasin B, but only partially inhibited by phlorizin. The reconstituted transporter also demonstrates trans-stimulation properties indicative of the carrier-mediated transport of D-glucose. In contrast to the human erythrocyte-type glucose transporter, in T. brucei D-fructose uptake was also catalyzed by the same reconstituted protein fraction and specific D-glucose or D-fructose transport were mutually competitive. Both the inhibitor studies and the fructose transport capacity in the reconstituted system are in good agreement with the native transport in live trypanosomes. The specific activity of D-glucose transport was 1.9 +/- 0.3 nmol.min-1.mg protein-1 at 0.2 mM D-glucose and the yield was about 0.8% of total ghost protein after removal of the variant-surface-glycoprotein coat. The successful functional reconstitution of a protozoan glucose transporter represents an important step towards its purification and detailed characterization. This is especially interesting since bloodstream-form trypanosomes depend entirely upon glycolysis for their ATP production.

Purification of a membrane glycoprotein with an inositol-containing phospholipid anchor from Dictyostelium discoideum

Large-scale purification of a Dictyostelium discoideum cell surface glycoprotein, which is anchored in the membrane via a glycosylphosphatidylinositol (GPI) moiety, is described. The purification protocol involved four steps: separation of crude cell membranes by low-speed centrifugation, delipidization of these membranes using acetone, extraction of the membrane proteins using the detergent Octyl beta-D-thioglucopyranoside (OTP), and purification of a specific membrane protein by monoclonal antibody immunoaffinity chromatography. The protein purified, PsA (prespore-specific antigen), is a developmentally regulated membrane glycoprotein found on a subset of cells from the cellular slime mould, D. discoideum. The protocol provides an efficient, economical, and technically simple way to purify GPI proteins in sufficient quantities for structural and functional studies. PsA was recovered at a yield of about 60%; with a purity of 97%, the extraction of 1 x 10(10) cells (1.1 g dry weight) yielded about 0.5 mg PsA glycoprotein. Techniques are described for growing kilogram quantities of D. discoideum cells in stainless steel trays at little cost. D. discoideum has considerable potential as a novel expression system for the production of foreign membrane-associated proteins. The purification strategy provides a means of purifying other GPI proteins, including those produced by protein engineering techniques.

The crystal structure of isobutyl 2,3,4-tri-O-acetyl-1-thio-beta-D-xylopyranoside

Isobutyl 2,3,4-tri-O-acetyl-1-thio-beta-D-xylopyranoside is monoclinic, P21, with a = 10.134(4), b = 7.748(3), c = 11.726(4) A, beta = 96.63(3) degrees, V = 914.55 A3, Z = 2, Dm = 1.262, Dx = 1.264 g . cm-3, mu(MoK alpha) = 226 M-1. The X-ray intensities of 1724 reflections were measured with Nb-filtered MoK alpha radiation (lambda = 0.7107 A) at room temperature. The structure was solved by direct methods, and refined by full-matrix least squares, with anisotropic thermal parameters for the carbon and oxygen atoms and isotropic thermal parameters for the hydrogen atoms, to a final agreement factor of R = 0.08. The molecule has the 4C1(D) conformation, with puckering parameters Q = 0.582 A, theta = 5.6 degrees, phi = 334.7 degrees. The acetyl groups have the planar, (S)-cis configuration most commonly observed. They are oriented, as in many other per-O-acetylated aldopyranosides, with the acetyl planes within +/- 30 degrees of the C-H bond at the ring-carbon atom to which they are attached. Although this is primarily a van der Waals structure, there is some evidence for CH---O hydrogen-bonding.

Use of n-octyl-beta-D-thioglucoside, a new nonionic detergent, for solubilization and reconstitution of membrane proteins

n-Octyl-beta-D-thioglucopyranoside (octylthioglucoside), a new nonionic detergent, was synthesized. Properties of this detergent and its applicability to membrane biochemistry were investigated. The critical micelle concentration of this detergent was determined to be 9 mM. Membrane proteins of Escherichia coli were effectively solubilized with octylthioglucoside at 25-35 mM. The solubilizing power was equivalent to that of n-octyl-beta-D-glucopyranoside (octylglucoside). Reconstitution of the melibiose carrier into liposomes was performed by the detergent dilution procedure. It was found that the concentration range of octylthioglucoside for successful reconstitution (45-70 mM) was considerably wider than that of octylglucoside (43-46 mM), thus giving more reproducible results. Octylthioglucoside is more stable than octylglucoside. Furthermore, the former is synthesized with high yield at low cost whereas the latter is very expensive. Thus, we conclude that octylthioglucose is superior to octylglucoside, and is very useful in membrane biochemistry.

The interaction of L-ascorbic acid with the active center of myrosinase

Only L-ascorbic acid activated plant myrosinase (thioglucoside glucohydrolase, EC 3.2.3.1), whereas ascorbic acid analogs did not. The enzyme protein was conformationally changed by the addition of L-ascorbic acid to the spectrophotometric analysis, approx. 1.5 amino residues appeared on the surface of the enzyme and about 2.3 tryptophan residues were buried in the molecule when 1 mM L-ascorbic acid was added. Optimum temperature for the myrosinase activity was approx. 55 degrees C without L-ascorbic acid, but with L-ascorbic acid it was about 35 degrees C; that for beta-glucosidase activity was the same (55 degrees C) with or without L-ascorbic acid. The effect of chemical modification of the functional groups of myrosinase on the interaction of L-ascorbic acid was investigated and the interaction of L-ascorbic acid with the active center of the enzyme is proposed.