Synthesis, characterization and application of two nucleoside triphosphate analogues, GTPgammaNH(2) and GTPgammaF.

Guanosine triphosphate nucleotide analogues such as GppNHp (also named GMPPNP) or GTPgammaS are widely used to stabilize rapidly hydrolyzing protein-nucleotide complexes and to investigate biochemical reaction pathways. Here we describe the chemical synthesis of guanosine 5'-O-(gamma-amidotriphosphate) (GTPgammaNH(2)) and a new synthesis of guanosine 5'-O-(gamma-fluorotriphosphate) (GTPgammaF). The two nucleotides were characterized using NMR spectroscopy and isothermal titration calorimetry. Chemical shift data on (31)P, (19)F and (1)H NMR resonances are tabulated. For GTPgammaNH(2) the enthalpy of magnesium coordination is DeltaH degrees = 3.9 kcal.mol(-1) and the association constant K(a) is 0.82 mm(-1). The activation energy for GTPgammaNH(2).Mg2+ complex formation is DeltaH++ = 7.8 +/- 0.15 kcal.mol(-1), similar to that for the natural substrate GTP. For GTPgammaF we obtained a similar enthalpy of DeltaH degrees = 3.9 kcal.mol(-1) while the magnesium association constant is only K(a) = 0.2 mm(-1). The application of both guanine nucleotide analogues to the GTP-binding protein Ras was investigated. The rate of hydrolysis of GTPgammaNH(2) bound to Ras protein lay between the rates found for Ras-bound GTPgammaS and GppNHp, while Ras-catalysed hydrolysis of GTPgammaF was almost as fast as for GTP. The two compounds extend the variety of nucleotide analogues and may prove useful in structural, kinetic and cellular studies.     

Phosphorothioate analogues of 5-phosphoribosyl 1-diphosphate: synthesis, purification, and partial characterization

The 1-phosphorothioate analogues of 5-phosphoribosyl 1-diphosphate (P-Rib-PP) have been prepared enzymatically, in reactions catalyzed by P-Rib-PP synthetase from Salmonella typhimurium. 5-Phosphoribosyl 1-O-(2-thiodiphosphate) (P-Rib-PP beta S) was synthesized from ribose 5-phosphate (Rib-5-P) and the Mg2+ complex of adenosine 5'-O-(3-thiotriphosphate). The SP and RP diastereomers of 5-phosphoribosyl 1-O-(1-thiodiphosphate) (P-Rib-PP alpha S) were synthesized from Rib-5-P and the Mg2+ complex of adenosine 5'-O-(2-thiotriphosphate) (ATP beta S) (SP diastereomer, delta-configuration) and the Cd2+ complex of ATP beta S (RP diastereomer, delta-configuration), respectively. The strategy for the synthesis and stereochemical assignment of the P-Rib-PP alpha S diastereomers was based on the specificity of P-Rib-PP synthetase for the (delta)-beta, gamma-bidentate metal-nucleotide substrate and the stereochemical course of the synthetase reaction, leading to inversion of configuration at the P beta atom of the nucleotide [Li, T. M., Mildvan, A. S., & Switzer, R. L. (1978) J. Biol. Chem. 253, 3918-3923], and the known configurations of the Mg2+ and Cd2+ beta, gamma-bidentate complexes of the ATP beta S diastereomers [Jaffe, E. K., & Cohn, M. (1979) J. Biol. Chem. 254, 10839-10845]. The P-Rib-PP analogues were purified by gradient elution from DEAE-Sephadex and characterized by chemical analysis and 31P nuclear magnetic resonance [Smithers, G. W., & O'Sullivan, W. J. (1984) Biochemistry (following paper in this issue)]. A preliminary account of their interaction with human brain hypoxanthine phosphoribosyltransferase and yeast orotate phosphoribosyltransferase (OPRTase) is described.(ABSTRACT TRUNCATED AT 250 WORDS)     

2-(Acyloxy)ethylphosphonate analogues of prenyl pyrophosphates: synthesis and biological characterization

2-(Acyloxy)ethylphosphonate analogues of geranyl, farnesyl, and geranylgeranyl pyrophosphate have been prepared. Horner–Wadsworth–Emmons condensation of different terpene aldehydes with an unsymmetrical bisphosphonate was the key step in syntheses of the phosphonates bearing ,β-unsaturated acyloxy groups. After preparation of the respective phosphonic acids through reaction with TMSBr, both acids and esters were tested for their effects on DNA synthesis in human-derived myeloid and lymphoid leukemia cell lines. The phosphonate esters varied substantially in their ability to impair proliferation of the different cell lines, but testing against one possible target, farnesyl protein transferase (FPTase), revealed little impact at concentrations ranging up to 10 μM. Because the corresponding 2,3-dihydro compounds showed similar biological activity, conjugate addition would not appear to be involved in the toxicity.     

Chemical synthesis, purification, and characterization of two inflammatory proteins, neutrophil activating peptide 1 (interleukin-8) and neutrophil activating peptide

Two recently identified pro-inflammatory proteins, namely, neutrophil activating peptide 1 (NAP-1) [also termed interleukin-8 (IL-8)] and NAP-2, were chemically synthesized, purified, and characterized. The fully protected NAP-1/IL-8 (72 residues) and NAP-2 (70 residues) peptide chains were assembled by automated solid-phase methods with average stepwise yields of 99.5 and 99.3%, resulting in overall chain assembly yields of 70 and 62%, respectively. Deprotection resulted in crude products, which were allowed to fold by air oxidation, and were purified by two cycles of reverse-phase high-pressure liquid chromatography, yielding 27 mg of NAP-1/IL-8 and 22 mg of NAP-2. Purity was established by reverse-phase high-pressure liquid chromatography and isoelectric focusing, and the primary structures of the purified products were verified by using mass spectrometry and Edman sequencing methods. Synthetic and recombinant NAP-1/IL-8 were equally active on human neutrophil granulocytes as determined by measuring the induction of cytosolic free calcium, elastase release, and chemotaxis. Synthetic NAP-2 was equivalent to purified natural NAP-2 in the elastase release and calcium mobilization assays, but it was consistently less potent (3-5-fold) as a stimulus of chemotaxis, perhaps indicative of additional chemotactic components in the natural preparation. The results indicate that by chemical synthesis these cytokines can be obtained in purity and quantities suitable for further structural analysis, as well as functional studies both in vivo and in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)     

Recombinant human CIS2 (SOCS2) protein: subcloning,expression, purification,and characterization

The 1x myc-tagged cDNA encoding for human CIS2 protein was subcloned into a pET-29a+ vector in order to express and produce a recombinant S-peptide tagged and 1x myc-tagged protein in Escherichia coli BL21(DE3). The constitutively expressed protein was isolated from inclusion bodies by a simple solubilization-renaturation procedure and purified by anion-exchange chromatography on Q-Sepharose. The recombinant form was found to be pure and monomeric as judged by both SDS-PAGE and gel-filtration chromatography and its biological activity was proven by its ability to bind to the tyrosine-phosphorylated cytosolic fragment of human growth hormone receptor fused to glutathione-S-transferase. Recombinant CIS2 was compared by biochemical, immunological, and molecular methods to the CIS2 protein expressed in eukaryotic cells. This report describes the first substantial production of biologically active recombinant human CIS2.     

Study in vitro and in vivo of nociceptin/orphanin FQ(1-13)NH2 analogues substituting N-Me-Gly for Gly2 or Gly3

In the present study, two analogues containing N-Me-Gly (Sarcosine, Sar) were synthesized to further investigate the structural-activity relationships of orphanin FQ/nociceptin (OFQ/NC, NC). The replacement of Gly(2) or Gly(3) with Sar increased the flexibility and decreased the hydrophobicity of the N-terminal tetrapeptide. The activity of the analogues was investigated in a series of assays in vivo and in vitro. [Sar(2)]NC(1-13)NH(2) was found to (1) produce dose-dependent inhibition of the electrically induced contraction in MVD assay (pEC(50) = 6.14); (2) produce significant hyperalgesia effects in a dose-dependent manner when intracerebroventricularly (i.c.v.) injected in mice. The inhibitive effects of [Sar(2)]NC(1-13)NH(2) in MVD assay could be significantly antagonized by [Nphe(1)]NC(1-13)NH(2), and partially antagonized by naloxone; the hyperalgesic effect of [Sar(2)]NC(1-13)NH(2) could be significantly antagonized by naloxone, and partially antagonized by [Nphe(1)]NC(1-13)NH(2). On the contrary, [Sar(3)]NC(1-13)NH(2) showed no effects in these assays. All the findings suggest that the flexibility of the peptide bond between Phe(1) and Gly(2) and between Gly(2) and Gly(3) play an important role in NC-OP(4) receptor interaction, and the hydrophobicity of the N-terminal tetrapeptide showed no significant effect on this interaction. The present work also helps to provide a novel method to elucidate structural and conformational requirements of the opioid peptide-receptor interaction.     

Ubiquitin: preparative chemical synthesis, purification and characterization

An improved total synthesis of ubiquitin has been achieved by the Fmoc/t-butyl solid-phase methodology using NGPmc protection of the Arg residues. Optimization of the purification protocol has offered the material in substantial quantity (90 mg) in an overall yield of 4.2%. Characterization of the isolated products has opened the way to the studies of the folding pathway and the preparation of structural analogues.     

Release, purification, and characterization of platelet-activating factor (PAF)

Platelet-activating factor (PAF) is a phospholipid mediator, released by basophils, macrophages and neutrophils under immunological and non immunological stimuli. It aggregates platelets and liberates their vasoactive contents. We studied the "spontaneous" release of PAF from hog blood leukocytes : optimal conditions were 22 degrees C, pH 9.5 in BSA and Ca2+-containing Tyrode's. This release was inhibited by the Ca2+-chelating agent, EDTA, and by the phospholipase A2 inhibitor, bromophenacyl bromide. Disruption of the cells did not yield PAF, indicating that it is not a "preformed" mediator. A preparative procedure for the extraction and purification of bulk quantities of PAF was developed. Purification was performed by silicic acid columns followed by high pressure liquid chromatography. The active fraction was eluted between sphingomyelin and lysophosphatidylcholine. The PAF purest fractions were still contaminated with these phospholipids as shown by thin layer chromatography and chemical ionization mass spectrometry. PAF activity was not affected by treatment with diazomethane, acetylation or hydrogenation. Our results combined with those obtained from our previous studies of the PAF structure using specific phospholipases indicate that PAF is a glycero-phospholipid devoid of ester function at position 1. This allowed us to establish precise criteria to distinguish PAF from other aggregating agents.     

Expression, purification, and characterization of a cobalt-activated chitin deacetylase (Cda2p) from Saccharomyces cerevisiae.

Chitin deacetylase (Cda2p) (EC 3.5.1.41) from Saccharomyces cerevisiae has been purified from vegetative cells grown in galactose and further characterized. The enzyme is a glycoprotein with an apparent molecular mass of approximately 43 kDa and a carbohydrate content of approximately 18% by weight. With glycol chitin as substrate, the optimum temperature for enzyme activity is 50 degrees C and the pH optimum is 8.0. The enzyme requires at least two N-acetyl-D-glucosamine residues (chitobiose) for catalysis and is partially inhibited by acetate. Deglycosylation of the enzyme causes total loss of enzyme activity, which can be restored by the addition of COCl(2).     

Novel C-ring analogues of 20(S)-camptothecin-part-2: synthesis and in vitro cytotoxicity of 5-C-substituted 20(S)-camptothecin analogues.

A series of 5-C-substituted 20(S)-camptothecin analogues were synthesised and evaluated their in vitro anti-cancer activity. Several of these analogues have showed excellent activity against human tumor cell lines.     

Functional consequences of alterations to Gly310, Gly770, and Gly801 located in the transmembrane domain of the Ca(2+)-ATPase of sarcoplasmic reticulum.

Site-specific mutagenesis was used to replace Gly310, Gly770, and Gly801, located in the transmembrane domain of the sarcoplasmic reticulum Ca(2+)-ATPase, with either alanine or valine. In addition, Gly310 was substituted with proline. In the Gly310----Ala mutant, the Vmax for Ca2+ transport and ATPase activity was reduced to about 40% of the wild type activity, but the apparent Ca2+ affinity was close to normal. The Gly310----Val and Gly310----Pro mutants were devoid of Ca2+ transport or ATPase activity and displayed more than a 20-fold reduction in the apparent Ca2+ affinities measured in the phosphorylation assays with either ATP or Pi. In these mutants, the rate of phosphoenzyme hydrolysis was reduced, and the ADP-insensitive phosphoenzyme intermediate accumulated. The apparent affinity for Pi was increased in the absence, but not in the presence, of dimethyl sulfoxide. The properties of this new class of Ca(2+)-ATPase mutants ("E2/E2P" type) are consistent with a conformational state in which the protein-phosphate interaction is stabilized and the Ca(2+)-protein interaction is destabilized. The Gly770----Ala mutant transported Ca2+ with a Vmax close to that of the wild type, but displayed more than a 20-fold reduction of apparent Ca2+ affinity. The Gly770----Val mutant was not phosphorylated from either ATP or Pi. The Gly801----Ala mutant transported Ca2+ with a Vmax of 126% that of the wild type, hydrolyzed ATP at the same Vmax as the wild type in the presence of calcium ionophore, and displayed a 3-fold reduction in apparent Ca2+ affinity. The Gly801----Val mutant was unable to transport Ca2+ and to be phosphorylated from ATP, even at a Ca2+ concentration of 1 mM, but Ca2+ in the micromolar range inhibited phosphorylation from Pi. The ability to bind ATP with normal affinity was retained. The properties of this mutant are consistent with a disruption of one of the two Ca2+ binding sites required for phosphorylation with ATP.     

Synthesis and purification of two SP (6-11) analogues with enhanced selectivity for the NK-1 receptor.

Two hexapeptide analogues of Substance P (6-11) have been synthesized. Replacement of Gly9 by proline provides a peptide with tenfold enhanced selectivity for the NK-1 receptor. The corresponding proline-containing glycopeptide incorporating a beta-D-glucopyranosyl residue linked to the side-chain of Glu6 was 100 times more selective than Substance P for the same receptor.     

Ostrich pancreatic phospholipase A(2): purification and biochemical characterization

Ostrich pancreatic phospholipase A(2) (OPLA(2)) was purified from delipidated pancreases. Pure protein was obtained after heat treatment (70 degrees C), precipitation by ammonium sulphate and ethanol, respectively followed by sequential column chromatography on MonoQ Sepharose and size exclusion HPLC column. Purified OPLA(2), which is not a glycosylated protein, was found to be monomeric protein with a molecular mass of 13773.93 Da. A specific activity of 840U/mg for purified OPLA(2) was measured at optimal conditions (pH 8.2 and 37 degrees C) in the presence of 4 mM NaTDC and 10 mM CaCl(2) using PC as substrate. This enzyme was also found to be able to hydrolyze, at low surface pressure, 1,2-dilauroyl-sn-glycero-3 phosphocholine (di C(12)-PC) monolayers. Maximal activity was measured at 5-8 mNm(-1). The sequence of the first 22 amino-acid residues at the N-terminal extremity of purified bird PLA(2) was determined by automatic Edman degradation and showed a high sequence homology with known mammal pancreatic secreted phospholipases A(2).     

Papain-like protease 2 (PLP2) from severe acute respiratory syndrome coronavirus (SARS-CoV): expression, purification, characterization, and inhibition

Viral proteases are essential for pathogenesis and virulence of severe acute respiratory syndrome coronavirus (SARS-CoV). Little information is available on SARS-CoV papain-like protease 2 (PLP2), and development of inhibitors against PLP2 is attractive for antiviral therapy. Here, we report the characterization of SARS-CoV PLP2 (from residues 1414 to 1858) purified from baculovirus-infected insect cells. We demonstrate that SARS-CoV PLP2 by itself differentially cleaves between the amino acids Gly180 and Ala181, Gly818 and Ala819, and Gly2740 and Lys2741 of the viral polypeptide pp1a, as determined by reversed-phase high-performance liquid chromatography analysis coupled with mass spectrometry. This protease is especially selective for the P1, P4, and P6 sites of the substrate. The study demonstrates, for the first time among coronaviral PLPs, that the reaction mechanism of SARS-CoV PLP2 is characteristic of papain and compatible with the involvement of the catalytic dyad (Cys)-S(-)/(His)-Im(+)H ion pair. With a fluorogenic inhibitor-screening platform, we show that zinc ion and its conjugates potently inhibit the enzymatic activity of SARS-CoV PLP2. In addition, we provided evidence for evolutionary reclassification of SARS-CoV. The results provide important insights into the biochemical properties of the coronaviral PLP family and a promising therapeutic way to fight SARS-CoV.