Protective effect of vaginal application of neutralizing and nonneutralizing inhibitory antibodies against vaginal SHIV challenge in macaques

Definition of antibody (Ab) functions capable of preventing mucosal HIV transmission may be critical to both effective vaccine development and the prophylactic use of monoclonal Abs. Although direct antibody-mediated neutralization is highly effective against cell-free virus, increasing evidence suggests an important role for immunoglobulin G (IgG) Fcγ receptor (FcγR)-mediated inhibition of HIV replication. Thus, a panel of well-known neutralizing (NAbs) and nonneutralizing Abs (NoNAbs) were screened for their ability to block HIV acquisition and replication in vitro in either an independent or FcγR-dependent manner. Abs displaying the highest Fc-mediated inhibitory activity in various in vitro assays were selected, formulated for topical vaginal application in a microbicide gel, and tested for their antiviral activity against SHIVSF162P3 vaginal challenge in non-human primates (NHPs). A combination of three NAbs, 2G12, 2F5, and 4E10, fully prevented simian/human immunodeficiency virus (SHIV) vaginal transmission in 10 out of 15 treated NHPs, whereas a combination of two NoNAbs, 246-D and 4B3, although having no impact on SHIV acquisition, reduced plasma viral load. These results indicate that anti-HIV Abs with distinct neutralization and inhibitory functions differentially affect in vivo HIV acquisition and replication, by interfering with early viral replication and dissemination. Therefore, combining diverse Ab properties may potentiate the protective effects of anti-HIV-Ab-based strategies.

High-resolution neutron protein crystallography with radically small crystal volumes: application of perdeuteration to human aldose reductase

Neutron diffraction data have been collected to 2.2 Angstrom resolution from a small (0.15 mm(3)) crystal of perdeuterated human aldose reductase (h-AR; MW = 36 kDa) in order to help to determine the protonation state of the enzyme. h-AR belongs to the aldo-keto reductase family and is implicated in diabetic complications. Its ternary complexes (h-AR-coenzyme NADPH-selected inhibitor) provide a good model to study both the enzymatic mechanism and inhibition. Here, the successful production of fully deuterated human aldose reductase [h-AR(D)], subsequent crystallization of the ternary complex h-AR(D)-NADPH-IDD594 and neutron Laue data collection at the LADI instrument at ILL using a crystal volume of just 0.15 mm(3) are reported. Neutron data were recorded to 2 Angstrom resolution, with subsequent data analysis using data to 2.2 Angstrom. This is the first fully deuterated enzyme of this size (36 kDa) to be solved by neutron diffraction and represents a milestone in the field, as the crystal volume is at least one order of magnitude smaller than those usually required for other high-resolution neutron structures determined to date. This illustrates the significant increase in the signal-to-noise ratio of data collected from perdeuterated crystals and demonstrates that good-quality neutron data can now be collected from more typical protein crystal volumes. Indeed, the signal-to-noise ratio is then dominated by other sources of instrument background, the nature of which is under investigation. This is important for the design of future instruments, which should take maximum advantage of the reduction in the intrinsic diffraction pattern background from fully deuterated samples.

Study on agglutinating factors from flocculent Saccharomyces cerevisiae strains

The lectin-like theory suggest that yeast flocculation is mediated by an aggregating lectinic factor. In this study we isolated an agglutinating factor, which corresponds to lectin, from whole cells by treating the flocculent wild-type Saccharomyces cerevisiae NCYC 625 strain and its weakly flocculent mutant [rho degrees ] with EDTA and two non-ionic surfactants (Hecameg and HTAC). The dialysed crude extracts obtained in this way agglutinated erythrocytes and this hemagglutination was specifically inhibited by mannose and mannose derivatives. However, SDS-PAGE profiles showed that the three reagents had different effects on the yeast cells. The non-ionic surfactants appeared to be the most efficient, as their extracts possessed the highest specific agglutinating activity. The products released by the wild-type strain presented a higher specific agglutinating activity than those released by the [rho degrees ] mutant. Purification of the agglutinating factor from extracts of both strains by affinity chromatography revealed two active bands of relative mass of 26 and 47 kDa on SDS-PAGE. Mass spectrometry analysis by MALDI-TOF, identified a 26 kDa band as the triose phosphate isomerase (TPI) whereas a 47 kDa band was identical to enolase. Edman degradation showed that the N-terminal sequences of these proteins were similar to TPI and enolase, respectively. The difference in the flocculation behaviour of the two strains is due to changes in the protein composition of the cell wall and in the protein structure involved in cell-cell recognition.

Expression, purification, crystallization and preliminary X-ray analysis of the cathelicidin motif of the protegrin-3 precursor

Numerous precursors of antibacterial peptides with unrelated sequences share a similar prosequence which belongs to the cathelicidin family of proteins. The three-dimensional structure of this cathelicidin motif, which contains two disulfide bonds, has not yet been reported. The cathelicidin motif (ProS) of the protegrin-3 precursor was overexpressed in Escherichia coli as a His-tagged protein. The His(6) tag was removed by thrombin cleavage. ProS was purified to homogeneity and single crystals were obtained by the hanging-drop vapour-diffusion method at pH 3-4. Preliminary X-ray diffraction analysis indicated that these crystals belong to the hexagonal space group P6(1)22 or P6(5)22, with unit-cell parameters a = b = 51.42, c = 134.25 A. These crystals diffracted beyond 2.75 A (1.9 A at ESRF) and contain one molecule per asymmetric unit.

Cost-effective and uniform (13)C- and (15)N-labeling of the 24-kDa N-terminal domain of the Escherichia coli gyrase B by overexpression in the photoautotrophic cyanobacterium Anabaena sp. PCC 7120

Structural studies of biomolecules using nuclear magnetic resonance (NMR) rely on the availability of samples enriched in (13)C and (15)N isotopes. While (13)C/(15)N-labeled proteins are generally obtained by overexpression in transformed Escherichia coli cells cultured in the presence of an expensive mixture of labeled precursors, those of the photoautotrophic cyanobacterium Anabaena sp. PCC 7120 can be uniformly labeled by growing them in medium containing Na(15)NO(3) and NaH(13)CO(3) as the sole nitrogen and carbon sources. We report here a novel vector-host system suitable for the efficient preparation of uniformly (13)C/(15)N-labeled proteins in Anabaena sp. PCC 7120. The 24-kDa N-terminal domain of the E. coli gyrase B subunit, used as a test protein, was cloned into the pRL25C shuttle vector under the control of the tac promoter. The transformed Anabaena cells were grown in the presence of the labeled mineral salts and culture conditions were optimized to obtain over 90% of (13)C and (15)N enrichment in the constitutively expressed 24-kDa polypeptide. The yield of purified 24-kDa protein after dual isotope labeling under anaerobic conditions was similar to that obtained with E. coli cells bearing a comparable expression vector and cultured in parallel in a commercially available labeling medium. Furthermore, as probed by NMR spectroscopy and mass spectrometry, the 24-kDa N-terminal domain expressed in Anabaena was identical to the E. coli sample, demonstrating that it was of sufficient quality for 3D-structure determination. Because the Anabaena system was far more advantageous taking into consideration the expense for the labels that were necessary, these results indicate that Anabaena sp. PCC 7120 is an economic alternative for the (13)C/(15)N-labeling of soluble recombinant proteins destined for structural studies.

Synthesis, mechanism of action, and antiviral activity of a new series of covalent mechanism-based inhibitors of S-adenosyl-L-homocysteine hydrolase

A direct method for the preparation of 5'-S-alkynyl-5'-thioadenosine and 5'-S-allenyl-5'-thioadenosine has been developed. Treatment of a protected 5'-acetylthio-5'-deoxyadenosine with sodium methoxide and propargyl bromide followed by deprotection gave the 5'-S-propargyl-5'-thioadenosine 4. Under controlled base-catalysis with sodium tert-butoxide in tert-butyl alcohol 4 was quantitatively converted into 5'-S-allenyl-5'-thioadenosine 5 or 5'-S-propynyl-5'-thioadenosine 6. Incubation of recombinant human placental AdoHcy hydrolase with 4, 5, or 6 resulted in time- and concentration-dependent inactivation of the enzyme (K(i): 45 +/- 0.5, 16 +/- 1, and 15 +/- 1 microM, respectively). Compound 4 caused complete conversion of the enzyme from its E-NAD(+) to E-NADH form during the inactivation process. This indicates that 4 is a substrate for the 3'-oxidative activity of AdoHcy hydrolase (type I inhibitor). In contrast, the NAD(+)/NADH content of the enzyme was not affected during the inactivation process with 5 and 6, and their mechanism of inactivation was further investigated. Addition of enzyme-sequestered water on the S-allenylthio group of 5 or S-propynylthio group of 6 within the active site should lead to the formation of the corresponding thioester 7. This acylating-intermediate agent could then undergo nucleophilic attack by a protein residue, leading to a type II mechanism-based inactivation. ElectroSpray mass spectra analysis of the inactivated protein by 5 supports this mechanistic proposal. Further studies (MALDI-TOF and ESI/MS(n) experiments) of the trypsin and endo-Lys-C proteolytic cleavage of the fragments of inactivated AdoHcy hydrolase by 5 were carried out for localization of the labeling. The antiviral activity of 4, 5, and 6 against a large variety of viruses was determined. Significant activity (EC(50): 1.9 microM) was noted with 5 against vaccinia virus.

Identification by mass spectrometry of two-dimensional gel electrophoresis-separated proteins extracted from lager brewing yeast

As two-dimensional (2-D) electrophoresis allows the separation of several hundred proteins in a single gel, this technique has become an important tool for proteome studies and for investigating the cellular physiology. In order to take advantage of information provided by the comparison of proteome pictures, the mass spectrometry technique is the way chosen for a rapid and an accurate identification of proteins of interest. Unfortunately, in the case of industrial yeasts, due to the high level of complexity of their genome, the whole DNA sequence is not yet available and all encoded protein sequences are still unknown. Nevertheless, this study presents here 30 lager brewing yeast proteins newly identified with matrix assisted laser desorption/ionization-time of flight (MALDI-TOF), tandem mass spectrometry (MS/MS) and database searching against the protein sequences of Saccharomyces cerevisiae. The identified proteins of the industrial strain correspond to proteins which do not comigrate with known proteins of S. cerevisiae separated on 2-D gels. This study presents an application of the MS technique for the identification of industrial yeast proteins which are only homologous to the corresponding S. cerevisiae proteins.

Synthesis and characterization of respiratory syncytial virus protein G related peptides containing two disulphide bridges

Respiratory Syncytial Virus (RSV) is the most important cause of bronchiolitis and viral pneumoniae in infants and young children. Approximately 100,000 children are hospitalized in the USA each year as a result of RSV infections. During the research and development of subunit human RSV vaccines, we have produced numerous synthetic peptides and recombinant proteins containing the four cysteines of the highly conserved central region of the G attachment protein. For several of these disulphide bridges containing peptides, all possible oxidizing isomers were synthesized using various oxidising conditions, resulting in different ratios of isomers. Each isolated isomer was fully characterized by RP-HPLC, FZCE and ES-MS after purification by preparative RP-HPLC. The different cysteine pairings were unambiguously established after enzymatic digestion, LC-MS analysis and peptide microsequencing. These synthetic and analytical methods were developed for the characterization of recombinant fusion protein BBG2Na which is currently investigated in clinical phase II and seems to be as a very promising vaccine candidate, and for peptides which were synthesized to be evaluated as conjugate vaccines or as immunochemical tools, after covalent coupling to carrier proteins. Furthermore, these studies allowed us to determine which of the different possible isomers was the most stable and probably the preferred form in native conditions. Finally, the different oxidising and analysis conditions, should be useful for disulphide pairing studies of other peptides and proteins having the same "xCxxCxxxxxCxxxCx" framework, such as G proteins of non-human RSV strains, developed for example as veterinary vaccine candidates.

Mass spectrometry as a novel approach to probe cooperativity in multimeric enzymatic systems

Investigating cooperativity in multimeric enzymes is of utmost interest to improve our understanding of the mechanism of enzymatic regulation. In the present article, we propose a novel approach based on mass spectrometry to probe cooperativity in the binding of a ligand to a multisubunit enzyme. This approach presents the selective advantage of giving a direct insight into all the subsequent ligation states that are formed in solution as the ligand is added to the enzyme. A quantitative interpretation of the electrospray ionization (ESI) mass spectra gives the relative abundance of all the distinct enzymatic species, which allows one to directly deduce the cooperativity of the system. The overall method is described for the addition of the oxidized cofactor nicotinamide adenine dinucleotide (NAD(+)) to a dimeric mutant of Bacillus stearothermophilus glyceraldehyde-3-phosphate dehydrogenase (GPDH). It is then applied to four tetrameric enzymes: sturgeon muscle GPDH, wild type and S48G mutant of GPDH from B. stearothermophilus, and alcohol dehydrogenase (ADH) from Bakers yeast. The results illustrate the possibilities offered by this new technique. First, mass spectrometry allows a control of the enzymes before the addition of NAD(+). Second, the cooperative behavior can be drawn from one single ESI mass spectrum, which makes the method highly attractive in terms of the amount of biological material required. Above all, the major benefit lies in the direct visualization of all the enzymatic species that are in equilibrium in solution. The direct measurement of cooperativity readily resolve the inconvenience of the classical approaches employed in this field, which all need to model the experimental data in order to get the cooperative behavior of the system.

Characterization and quality control of recombinant adenovirus vectors for gene therapy

Highly purified recombinant adenovirus undergoes routine quality controls for identity, potency and purity prior to its use as a gene therapy vector. Quantitative characterization of infectivity is measurable by the expression of the DNA binding protein, an early adenoviral protein, in an immunofluorescence bioassay on permissive cells as a potency determinant. The specific particle count, a key quality indicator, is the total number of intact particles present compared to the number of infectious units. Electron microscopic analysis using negative staining gives a qualitative biophysical analysis of the particles eluted from anion-exchange HPLC. One purity assessment is accomplished via the documented presence and relative ratios of component adenoviral proteins as well as potential contaminants by reversed-phase HPLC of the intact virus followed by protein peak identification using MALDI-TOF mass spectrometry and subsequent data mining. Verification of the viral genome is performed and expression of the transgene is evaluated in in vitro systems for identity. Production lots are also evaluated for replication-competent adenovirus prior to human use. For adenovirus carrying the human IL-2 transgene, quantitative IL-2 expression is demonstrated by ELISA and cytokine potency by cytotoxic T lymphocyte assay following infection of permissive cells. Both quantitative and qualitative analyses show good batch to batch reproducibility under routine test conditions using validated methods.

Self-assembly of a diferrous triple-stranded helicate with bis(2,2'-bipyridine) ligands: thermodynamic and kinetic intermediates

The protonation and iron(II) coordination properties of a bis(2,2'-bipyridine) ligand L were investigated in methanol. The protonated forms showed allosteric effects due to the flexibility of the strand. Speciation studies of the corresponding ferrous complexes were carried out as a function of pH and iron(II) concentrations. A combination of electrospray mass spectroscopy, potentiometry, and spectrophotometry allowed the determination in solution of three ferrous complexes, one mononuclear (L2Fe2+) and two dinuclear (L2Fe2(4+) and L3Fe2(4+)) species. Their structure was deduced from the metal spin state and confirmed by 1H NMR measurements and molecular modeling. The dissociation process of the triple-stranded diferrous helicate L3Fe2(4+) by OH- revealed two rate-limiting steps. The former leads to the formation of a monoferrous triple-stranded compound via a classical mechanism, which involves hydroxy-ferrous complexes. A similar process was observed in the latter step for the release of the ferrous cation from the mononuclear intermediate. Taking into account the structural, thermodynamic, and kinetic features provided by the present study, we could propose a self-assembling mechanism of the triple-stranded diferrous helicate.

Characterization of crystal content by ESI-MS and MALDI-MS

A general approach based on mass spectrometry is described for the rapid identification of the content of macromolecular crystals. The experimental procedure was established using lysozyme crystals and then successfully applied to various systems containing specifically bound molecules not easily detectable by other classical techniques. This procedure can be carried out on crystals containing macromolecules of a different nature, such as proteins, nucleic acids and small organic molecules and their non-covalent complexes, grown under various crystallization conditions including PEGs and salts. It can be applied very early on in the crystallization process - as soon as the crystals can be handled. It allows the biologist to control precisely the sequence integrity and homogeneity of the crystallized proteins (in particular at the C-terminus) as well as to verify whether the protein has crystallized with all its expected partners or ligands (nucleic acid molecules, cofactor or small organic molecules).

Aldose and aldehyde reductases: correlation of molecular modeling and mass spectrometric studies on the binding of inhibitors to the active site

Aldose and aldehyde reductases are monomeric NADPH-dependent oxidoreductases that catalyze the reduction of a wide variety of aldehydes and ketones to their corresponding alcohols. The overall three-dimensional structures of the enzymes are composed of similar alpha/beta TIM-barrels, and the active site residues Tyr 50, His 113, and Trp 114 interacting with the hydrophilic heads of inhibitors are conserved. We have used molecular modeling and mass spectrometry to characterize the interactions between the enzymes and three aldose reductase inhibitors: tolrestat, sorbinil, and zopolrestat. Unlike the IC(50) values (concentration of inhibitor giving 50% of inhibition in solution), the Vc(50) values measured by mass spectrometry (accelerating voltage of ions needed to dissociate 50% of a noncovalent complex in the gas phase) for the two enzymes are similar, and they correlate with the electrostatic and hydrogen-bonding energies calculated between the conserved Tyr 50, His 113, and Trp 114 and the inhibitors. The results of our comparison agree with detailed structural information obtained by X-ray crystallography, suggesting that nonconserved residues from the C-terminal loop account for differences in IC(50) values for the two enzymes. Additionally, they confirm our previous assumption that the Vc(50) values reflect the enzyme-inhibitor electrostatic and hydrogen-bonding interactions and exclude the hydrophobic interactions.

Structural characterization of the cysteine-rich domain of TFIIH p44 subunit

In an effort to understand the structure function relationship of TFIIH, a transcription/repair factor, we focused our attention on the p44 subunit, which plays a central role in both mechanisms. The amino-terminal portion of p44 has been shown to be involved in the regulation of the XPD helicase activity; here we show that its carboxyl-terminal domain is essential for TFIIH transcription activity and that it binds three zinc atoms through two independent modules. The first contains a C4 zinc finger motif, whereas the second is characterized by a CX(2)CX(2-4)FCADCD motif, corresponding to interleaved zinc binding sites. The solution structure of this second module reveals an unexpected homology with the regulatory domain of protein kinase C and provides a framework to study its role at the molecular level.

Calcium-induced noncovalently linked tetramers of MRP8 and MRP14 are confirmed by electrospray ionization-mass analysis

Proteins of the S100- family such as MRP8 (S100A8) and MRP14 (S100A9)-and its isoform MRP14*-show two calcium-binding sites (EF hands) per protein chain. MRP8, MRP14*, and MRP14, isolated from human granulocytes or monocytes, are known to form noncovalently associated complexes; the exact stoichiometries of these complexes in the presence of calcium are still controversially discussed in the literature. The present electrospray ionization-mass spectrometry (ESI-MS) study shows that MRP8, MRP14*, and MRP14 exist as heterodimers MRP8/14* and MRP8/14, respectively, in the absence of calcium confirming both a recent nuclear magnetic resonance study and a biochemical study on this topic. Furthermore, this ESI-MS study confirms the previously published matrix-assisted laser desorption ionization (MALDI)-MS study, which states that the MRP8/14* and MRP8/14 heterodimeric complexes tetramerize to heterotetramers (MRP8/14*)2, (MRP8/14*)(MRP8/14), and (MRP8/14)2, respectively, in the presence of calcium. The number of Ca2+ ions bound to the individual tetramer is determined to be eight for nonphosphorylated fractions; this is in agreement with the previously reported MALDI study on these fractions. About 1.2 Ca2+ ions more are bound to the phosphorylated form; it is speculated that the additional Ca2+ ions are bound to the phosphate groups in the tetramers. This study is, therefore, convincing proof of the reliability of MALDI-MS in studying noncovalent protein-protein interactions.

Determination by electrospray mass spectrometry of the outersphere association constants of DNA/platinum complexes using 20-mer oligonucleotides and ([Pt(NH(3))(4)](2+), 2Cl(-)) or ([Pt(py)(4)](2+), 2Cl(-))

The cytotoxic effects of cisplatin, cis-diamminedichloroplatinum(II), are generally ascribed to the formation of DNA adducts. Several in vitro as well as in vivo studies showed that cisplatin binds preferentially to guanines belonging to (G)(n) sequences (n > or = 2). After mono- or diaquation of cisplatin, giving the cationic complexes cis-[PtCl(NH(3))(2)(H(2)O)](+) and cis-[Pt(NH(3))(2)(H(2)O)(2)](2+), DNA platination occurs in two steps: the cationic complex gives an outersphere association with DNA and the actual coordination then occurs by substitution of one aqua ligand by guanine-N7. For a better understanding of the (G)(n) selectivity of cisplatin giving the biologically active adducts, also necessary for the conception of new platinum drugs, the respective contribution of the outersphere association and actual guanine platination must be investigated. To check the role of outersphere association in the overall platination process, we used electrospray mass spectrometry (ESMS) to detect and quantify outersphere association between 20-mer oligonucleotides and platinum complexes. The 20-mer oligonucleotides were single- or double-stranded, with the same number of guanines either isolated or adjacent to each other. To deal only with outersphere association and check the influence of platinum ligands, the [Pt(NH(3))(4)](2+) and [Pt(py)(4)](2+) complexes were used. We characterized by ESMS all the different outersphere association species formed during titration of each oligonucleotide with the various platinum complexes and evaluated their affinity constants. The ESMS results demonstrate that the outersphere association depends on electrostatic interactions and on the ability of the platinum ligands to participate to hydrogen bonding, particularly within the duplex form.

Characterization of a new electrophoretically silent hemoglobin variant. Hb saale OR alpha 2beta 2 84(EF8)Thr --> Ala

A new abnormal hemoglobin was detected in a young German anemic patient by cation-exchange high performance liquid chromatography (HPLC). Using a combination of electrospray mass spectrometry, HPLC, direct sequencing, and family screening with polymerase chain reaction/restriction digestion approach, we have characterized this hemoglobin variant as resulting from a Thr --> Ala replacement at beta84(EF8). It could be separated neither by electrophoresis nor by isoelectric focusing. Hb Saale is slightly unstable, exhibiting a moderate tendency to auto-oxidize. Functional properties and the heterotropic interactions are similar to those of Hb A.

Heterodimeric complex of RAR and RXR nuclear receptor ligand-binding domains: purification, crystallization, and preliminary X-ray diffraction analysis

Both the human retinoic acid receptor alpha (hRARalpha) and a constitutively active mutant (F318A) of the mouse retinoid X receptor alpha (mRXR alpha F318A) ligand-binding domains were separately overexpressed in Escherichia coli, copurified as a heterodimer in a two-step procedure, and cocrystallized with an RAR alpha-specific antagonist by using polyethylene glycol 10,000 as precipitant. The crystals grew in the hexagonal space group P6(1)22 displaying the unit cell parameters a = b = 116.6 A and c = 207.8 A. They diffracted X-ray to a limit of 2.2-A resolution. The asymmetric unit comprises one heterodimer and the crystal contains 60% solvent. The structure was determined by molecular replacement and is currently being refined.

Nitrous oxide fraction in the carbon dioxide pneumoperitoneum during laparoscopy under general inhaled anesthesia in pigs

During prolonged laparoscopy, the diffusion of other gases in the carbon dioxide (CO(2)) pneumoperitoneum may lessen its safety. Nitrous oxide (N(2)O)/CO(2) gas mixtures may become hazardous with regard to gas embolization and fire risk. We therefore evaluated the kinetics of pneumoperitoneal intrusion of N(2)O. In five anesthetized domestic pigs, controlled ventilation, with an initial fraction of inspired oxygen = 1.0, was adjusted to keep ETCO(2) pressure between 35 and 45 mm Hg. The peritoneum was insufflated with CO(2) to a pressure of 12 mm Hg, which was maintained throughout the procedure. T0 was defined as the time when N(2)O was introduced in the breathing circuit (N(2)O end-tidal fraction = 66%). Gas samples (10 mL) from the pneumoperitoneum were analyzed every 10 min after T0. The N(2)O concentration was measured by using capillary gas chromatography coupled with mass spectrometry. Percentages of N(2)O in the CO(2) increased with time (t) according to the ideal equation: N(2)O((t)) = 66 (1 - exp(-0.005t)). In the peritoneal cavity, <2 h were required for the N(2)O to reach the concentration of 29%, which can support combustion. Eight hours to 10 h after T0, the intraperitoneal N(2)O fraction approaches the level of the N(2)O end-tidal fraction. Options to prevent accumulation of N(2)O are suggested.

IMPLICATIONS

Pig models were used to evaluate the time course of nitrous oxide (N(2)O) diffusion in the pneumoperitoneum during nitrous oxide/oxygen anesthesia. Although peritoneal N(2)O concentration approaches the end-expiratory value after 8-10 h, it reaches 29% within 2 h. At this level, N(2)O is known to support combustion. This N(2)O pollution should be prevented.

Synthesis and characterization of Respiratory Syncytial Virus protein G related peptides containing two disulfide bridges

Respiratory Syncytial Virus (RSV) is the most important cause of bronchiolitis and viral pneumonia in infants and young children. Approximately 100000 children are hospitalized in the USA each year as a result of RSV infections. During the research and development of subunit human Respiratory Syncytial Virus vaccines (hRSV), we have produced numerous synthetic peptides and recombinant proteins containing the four cysteines of the highly conserved central region of the G attachment protein. For several of these disulfide-containing peptides, all possible oxidized isomers were synthesized using various oxidation conditions and resulting in different ratios of isomers. Each isolated isomer was fully characterized by RP-HPLC, FZCE and ES-MS after purification by preparative RP-HPLC. The different cysteine pairings were unambiguously established after enzymatic digestion, LC-MS analysis and peptide microsequencing. These synthesis and analytical methods were developed for the characterization on one hand, of recombinant fusion protein BBG2Na which is currently being investigated in advanced clinical phases as a very promising vaccine candidate, and on the other hand, for peptides which were synthesized to be evaluated as conjugate vaccines or as immunochemical tools, after covalent coupling to carrier proteins. Furthermore, these studies allowed us to determine which of the different possible isomers was the most stable and probably the preferred form in native conditions. Finally, the different oxidation and analysis conditions, should be useful for disulfide pairing studies of other peptides and proteins having the same 'xCxxCxxxxxCxxxCx' framework, such as G proteins of non-human RSV strains, developed by other groups as veterinary vaccine candidates for example.

Recombinant expression and range of activity of penaeidins, antimicrobial peptides from penaeid shrimp

Penaeidins are 5.5- to 6.6-kDa antimicrobial peptides recently isolated from the plasma and haemocytes of the tropical shrimp Penaeus vannamei. These molecules differ from the other classes of antimicrobial peptides in that they are composed of a proline-rich N-terminus and of a C-terminus containing six cysteine residues engaged in three disulfide bridges. In order to gain information on their antimicrobial activity, two penaeidins (Pen-2 and Pen-3a) were expressed in Saccharomyces cerevisiae. The recombinant Pen-2 and -3a were characterized in terms of primary structure by Edman degradation, mass spectrometry and gas chromatography. A protocol was then established to purify the amount of penaeidins required for the determination of their activity spectrum. We demonstrate in this study that expression in yeast is appropriate for the large-scale production of functional penaeidins, whose activities are almost indistinguishable from those of the native molecules. Data on Pen-2 and -3a activity demonstrate that penaeidins have a broad spectrum of antifungal properties associated with a fungicidal activity, and that their antibacterial activities are essentially directed against Gram-positive bacteria, with a strain-specific inhibition mechanism. Despite a better efficiency of Pen-3a on most of the tested strains, similar activity spectra and inhibition mechanisms were observed for both Pen-2 and -3a. Finally, no synergistic effect could be observed between the two molecules.

Profiling the peptides in two neurohemal organs, the sinus gland and lateral nervous plexus of terrestrial isopods (Crustacea), by mass spectrometry

A comparison was made of the ultrastructure of two neurohemal organs: the sinus gland and the lateral nervous plexus of the Oniscidea (Crustacea). Reverse-phase chromatography clearly showed that the two organs contain different neuropeptides. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry proved to be an efficient tool for detecting the molecules stored in a single freshly dissected neurohemal organ. All the results combined lead us to emphasize that the sinus gland of Oniscidea stores mainly crustacean hyperglycemic hormone (CHH) and vitellogenin-inhibiting hormone; these two hormones were not characterized in the lateral nervous plexus (LNP). Smaller peptides and other molecules of the CHH family might be released by the LNP in the vicinity of the Y-organ (the ecdysteroid-producing gland).

Isolation and amino acid sequence of a peptide with vitellogenesis inhibiting activity from the terrestrial isopod Armadillidium vulgare (Crustacea)

The complete amino acid sequence of a neuropeptide was established using gas-phase microsequencing, mass spectrometry, and reverse transcription-polymerase chain reaction. This peptide, stored in the sinus gland of the terrestrial isopod Armadillidium vulgare, inhibited vitellogenin synthesis by the fat tissue and inhibited the onset of secondary vitellogenesis when tested in homologous bioassays. This peptide, named Arv-VIH, has 83 amino acid residues and a molecular mass of 9485 Da. Relationships with other related peptides are presented.

Matrix-assisted laser desorption ionization mass spectrometry: a new tool for probing interactions between proteins and metal surfaces. Use in dental implantology

The fixation in the bone of an artificial titanium tooth root is believed to be initiated by the rapid adsorption of the proteins present in the surgical cavity on the titanium surface. The study of this adsorption should make it possible to predict the osseointegration capacities of new implant surface treatments. We describe here a new method, based on matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS), for quantifying proteins adsorbed on titanium surfaces fully identical to these designed for implantology. The key step of this method is a new MALDI-MS sample preparation allowing the adsorbed proteins to be removed from the surface and to be homogeneously dispersed in the matrix crystals. The adsorption of a model protein (lysozyme) on two titanium surfaces (polished and sandblasted) was studied in order to evaluate the method. The absolute MALDI-MS intensity was shown to vary linearly with the amount of adsorbed lysozyme. After dipping the titanium surfaces for different times in lysozyme solutions at different concentrations, the maximum amount of adsorbed lysozyme was measured by MALDI-MS and was shown to correspond to a lysozyme monolayer, which is consistent with results described in the literature.

Binding of aldose reductase inhibitors: correlation of crystallographic and mass spectrometric studies

Aldose reductase is a NADP(H)-dependent enzyme, believed to be strongly implicated in the development of degenerative complications of Diabetes Mellitus. The search for specific inhibitors of this enzyme has thus become a major pharmaceutic challenge. In this study, we applied both X-ray crystallography and mass spectrometry to characterize the interactions between aldose reductase and four representative inhibitors: AminoSNM, Imirestat, LCB3071, and IDD384. If crystallography remains obviously the only way to get an extensive description of the contacts between an inhibitor and the enzymatic site, the duration of the crystallographic analysis makes this technique incompatible with high throughput screenings of inhibitors. On the other hand, dissociation experiments monitored by mass spectrometry permitted us to evaluate rapidly the relative gas-phase stabilities of the aldose reductase-inhibitor noncovalent complexes. In our experiments, dissociation in the gas-phase was provoked by increasing the accelerating voltage of the ions (Vc) in the source-analyzer interface region: the Vc value needed to dissociate 50% of the noncovalent complex initially present (Vc50) was taken as a gas-phase stability parameter of the enzyme-inhibitor complex. Interestingly, the Vc50 were found to correlate with the energy of the electrostatic and H-bond interactions involved in the contact aldose reductase/inhibitor (Eel-H), computed from the crystallographic model. This finding may be specially interesting in a context of drug development. Actually, during a drug design optimization phase, the binding of the drug to the target enzyme is often optimized by modifying its interatomic electrostatic and H-bond contacts; because they usually depend on a single atom change on the drug, and are easier to introduce than the hydrophobic interactions. Therefore, the Vc50 may help to monitor the chemical modifications introduced in new inhibitors. X-ray crystallography is clearly needed to get the details of the contacts and to rationalize the design. Nevertheless, once the cycle of chemical modification is engaged, mass spectrometry can be used to select a priori the drug candidates which are worthy of further crystallographic investigation. We thus propose to use the two techniques in a complementary way, to improve the screening of large collections of inhibitors.

Phosphorylation of the myristoylated protein kinase C substrate MARCKS by the cyclin E-cyclin-dependent kinase 2 complex in vitro

The myristoylated alanine-rich C-kinase substrate (MARCKS) purified from brain was recently characterized as a proline-directed kinase(s) substrate in vivo [Taniguchi, Manenti, Suzuki and Titani (1994) J. Biol. Chem. 269, 18299-18302]. Here we have investigated the phosphorylation of MARCKS by various cyclin-dependent kinases (Cdks) in vitro. We established that Cdk2, Cdk4 and, to a smaller extent, Cdk1 that have been immunoprecipitated from cellular extracts phosphorylate MARCKS. Comparison of MARCKS phosphorylation by protein kinase C (PKC) and by the purified cyclin E-Cdk2 complex suggested that two residues were phosphorylated by Cdk2 under these conditions. To identify these sites, Cdk2-phosphorylated MARCKS was digested with lysyl endoprotease and analysed by electrospray MS. Comparison with the digests obtained from the unphosphorylated protein demonstrated that two peptides, Gly12-Lys30 and Ala138-Lys152, were phosphorylated by cyclin E-Cdk2. The identity of these peptides was confirmed by automatic Edman degradation. On the basis of the consensus phosphorylation sequence described for Cdk2, and on MS/MS analysis of the Ala138-Lys152 peptide, we concluded that Ser27, one of the phosphorylation sites identified in vivo, and Thr150 were the Cdk2 targets in vitro. None of the other sites described in vivo were phosphorylated in these conditions. Interestingly, a preliminary phosphorylation of MARCKS by PKC improved the initial rate of phosphorylation by Cdk2 without modifying the number of sites concerned. In contrast, phosphorylation of MARCKS by Cdk2 did not significantly affect further phosphorylation by PKC.

The structure of a glycosylated protein hormone responsible for sex determination in the isopod, Armadillidium vulgare

Two glycoforms (AH1 and AH2) of androgenic hormone, and its corresponding hormone precursor derived from HPLC-purified androgenic gland extract from the woodlouse Armadillidium vulgare were fully characterized by microsequencing and mass spectrometry. The amino-acid sequences of the two glycoforms were identical; they consist of two peptide chains, A and B, of 29 and 44 amino acids, respectively, with chain A carrying one N-glycosylated moiety on Asn18. The two chains are linked by two disulfide bridges. Glycoforms were only differentiated by the size and heterogeneity of the glycan chain. The androgenic hormone precursor (16.5 kDa) was shown to contain the sequence of chains A and B from the androgenic hormone, connected by a C-peptide (50 amino acids). These results were confirmed by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) analysis performed on a single hypertrophied androgenic gland. When injected into young females, both glycoforms of the androgenic hormone were able to override genetic sex-determination. In invertebrates, there is no other example where sex-differentiation is controlled by a protein hormone that is not synthesized by the gonads but by a special gland. A functional comparison with two other hormones which are believed to play a role in sex determination, i.e. ecdysone in insects and anti-Müllerian hormone in mammals, is presented. Work is in progress to clone and characterize the gene encoding androgenic hormone, moreover special attention is devoted to its regulatory regions, putative targets for the Wolbachia action.

Production of crystals of human aldose reductase with very high resolution diffraction

As the action of human aldose reductase (hAR) is thought to be linked to the pathogenesis of diabetic complications, much effort has been directed towards the analysis of the catalytic mechanism and the development of specific inhibitors. Here, the crystallization of recombinant hAR with its cofactor NADP+ at 277 K in the presence of the precipitating agent PEG 6000 is reported. The crystals diffract to high resolution (1.1 A) and belong to the P21 space group with unit-cell parameters a = 49.97, b = 67.14, c = 48. 02 A, beta = 92.2 degrees with one molecule per asymmetric unit. Seleno-substituted hAR crystals were also produced and diffract to 1. 7 A on a conventional X-ray source.

Aah VI, a novel, N-glycosylated anti-insect toxin from Androctonus australis hector scorpion venom: isolation, characterisation, and glycan structure determination

Aah VI was isolated from the venom of the North African scorpion, Androctonus australis hector. It is the first glycosylated neurotoxin from scorpion venom to be described. It was not toxic to mice, when injected intracerebroventricularly at a dose of 1.2 microg per animal. However, it had typical activity in Blatella germanica cockroaches resulting in gradual paralysis and very low toxicity (LD50 = 8.5 microg/g of animal). It consists of 66 amino acid residues and is heterogeneously N-glycosylated at a single site, on asparagine 9, of the Asn-Gly-Thr sequence. The potential N-glycosylation site was deduced from automatic Edman degradation and amino acid analysis, and glycan heterogeneity was evidenced by ESMS. Determination of the N-glycan structures (dHex, Hex and HexNAc) was assessed by nanoESMS/MS with picomolar amounts of sample. Current knowledge of N-glycan structure and composition suggests that the glycan structures are derived from a common core.

Phosphorylation and O-glycosylation sites of human chromogranin A (CGA79-439) from urine of patients with carcinoid tumors

Because of their water-soluble properties, chromogranins (CGs) and chromogranin-derived fragments are released together with catecholamines from adrenal chromaffin cells during stress situations and can be detected in the blood by radiochemical and enzyme assays. It is well known that chromogranins can serve as immunocytochemical markers for neuroendocrine tissues and as a diagnostic tool for neuroendocrine tumors. In 1993, large CGA-derived fragments have been shown to be excreted into the urine in patients with carcinoid tumors and the present study deals with the characterization of the post-translational modifications (phosphorylation and O-glycosylation) located along the largest natural CGA-derived fragment CGA79-439. Using mild proteolysis of peptidic material, high performance liquid chromatography, sequencing, and mass spectrometry analysis, six post-translational modifications were detected along the C-terminal CGA-derived fragment CGA79-439. Three O-linked glycosylation sites were located in the core of the protein on Thr163, Thr165, and Thr233, consisting in di-, tri-, and tetrasaccharides. Three phosphorylation sites were located in the middle and C-terminal domain, on serine residues Ser200, Ser252, and Ser315. These modified sites were compared with sequences of others species and discussed in relation with the post-translational modifications that we have reported previously for bovine CGA.

Substituting selenocysteine for active site cysteine 149 of phosphorylating glyceraldehyde 3-phosphate dehydrogenase reveals a peroxidase activity

Replacing the essential Cys-149 by a selenocysteine into the active site of phosphorylating glyceraldehyde 3-phosphate dehydrogenase (GAPDH) from Bacillus stearothermophilus leads to a selenoGAPDH that mimics a selenoperoxidase activity. Saturation kinetics were observed with cumenyl and tert-butyl hydroperoxides, with a better catalytic efficiency for the aromatic compound. The enzymatic mechanism fits a sequential model where the formation of a ternary complex between the holoselenoenzyme, the 3-carboxy 4-nitrobenzenethiol used as the reductant and the hydroperoxide precedes product release. The fact that the selenoGAPDH is NAD-saturated supports a binding of hydroperoxide and reductant in the substrate binding site. The catalytic efficiency is similar to selenosubtilisins but remains low compared to selenoglutathione peroxidase. This is discussed in relation to what is known from the X-ray crystal structures of selenoglutathione peroxidase and GAPDHs.

Characterization of antibacterial COOH-terminal proenkephalin-A-derived peptides (PEAP) in infectious fluids. Importance of enkelytin, the antibacterial PEAP209-237 secreted by stimulated chromaffin cells

Proenkephalin-A (PEA) and its derived peptides (PEAP) have been described in neural, neuroendocrine tissues and immune cells. The processing of PEA has been extensively studied in the adrenal medulla chromaffin cell showing that maturation starts with the removal of the carboxyl-terminal PEAP209-239. In 1995, our laboratory has shown that antibacterial activity is present within the intragranular chromaffin granule matrix and in the extracellular medium following exocytosis. More recently, we have identified an intragranular peptide, named enkelytin, corresponding to the bisphosphorylated PEAP209-237, that inhibits the growth of Micrococcus luteus (Goumon, Y., Strub, J. M., Moniatte, M., Nullans, G., Poteur, L., Hubert, P., Van Dorsselaer, A., Aunis, D., and Metz-Boutigue, M. H. (1996) Eur. J. Biochem. 235, 516-525). As a continuation of this previous study, in order to characterize the biological function of antibacterial PEAP, we have here examined whether this COOH-terminal fragment is released from stimulated chromaffin cells and whether it could be detected in wound fluids and in polymorphonuclear secretions following cell stimulation. The antibacterial spectrum shows that enkelytin is active against several Gram-positive bacteria including Staphylococcus aureus, but it is unable to inhibit the Gram-negative bacteria growth. In order to relate the antibacterial activity of enkelytin with structural features, various synthetic enkelytin-derived peptides were tested. We also propose a computer model of synthetic PEAP209-237 deduced from 1H NMR analysis, in order to relate the antibacterial activity of enkelytin with the three-dimensional structure. Finally, we report the high phylogenetic conservation of the COOH-terminal PEAP, which implies some important biological function and we discuss the putative importance of enkelytin in the defensive processes.

Hemoglobin Rambam (β69[E13]Gly→Asp), a pitfall in the assessment of diabetic control: characterization by electrospray mass spectrometry and HPLC

Hemoglobin (Hb) Rambam, or β69[E13]Gly→Asp, has been identified in a German woman also suffering from non-insulin-dependent diabetes mellitus and chronic obstructive pulmonary disease. This is the first observation of this Hb variant in a German family thus far. The detailed evaluation of its structure using electrospray mass spectrometry revealed new minor glycohemoglobin components and showed that the attachment of glucose to the β NH2 terminus occurred at an almost identical rate in both wild-type and mutant β-chains. However, the introduction of a carboxyl group at β69 seems to increase the glycation of ε-amino groups of lysine residues. The glycemic state in the propositus was well reflected by the total glycohemoglobin concentrations but not by the Hb A1C values, which did not reflect hemoglobin glycation in this patient. This case demonstrates that Hb A1C cannot be used reliably in the management of diabetic patients carrying Hb variants such as Hb Rambam. Functional studies of the whole blood of the heterozygous carrier demonstrated extremely low oxygen affinity, which may have been caused by increased 2,3-diphosphoglycerate related to chronic obstructive pulmonary disease and hyperthyroidism. None of the clinical symptoms could be directly associated to Hb Rambam.

Hemoglobin Rambam (beta69[E13]Gly-->Asp), a pitfall in the assessment of diabetic control: characterization by electrospray mass spectrometry and HPLC

Hemoglobin (Hb) Rambam, or beta69[E13]Gly-->Asp, has been identified in a German woman also suffering from non-insulin-dependent diabetes mellitus and chronic obstructive pulmonary disease. This is the first observation of this Hb variant in a German family thus far. The detailed evaluation of its structure using electrospray mass spectrometry revealed new minor glycohemoglobin components and showed that the attachment of glucose to the beta NH2 terminus occurred at an almost identical rate in both wild-type and mutant beta-chains. However, the introduction of a carboxyl group at beta69 seems to increase the glycation of epsilon-amino groups of lysine residues. The glycemic state in the propositus was well reflected by the total glycohemoglobin concentrations but not by the Hb A1c values, which did not reflect hemoglobin glycation in this patient. This case demonstrates that Hb A1c cannot be used reliably in the management of diabetic patients carrying Hb variants such as Hb Rambam. Functional studies of the whole blood of the heterozygous carrier demonstrated extremely low oxygen affinity, which may have been caused by increased 2,3-diphosphoglycerate related to chronic obstructive pulmonary disease and hyperthyroidism. None of the clinical symptoms could be directly associated to Hb Rambam.

Differential display of peptides induced during the immune response of Drosophila: a matrix-assisted laser desorption ionization time-of-flight mass spectrometry study

We have developed an approach based on a differential mass spectrometric analysis to detect molecules induced during the immune response of Drosophila, regardless of their biological activities. For this, we have applied directly matrix-assisted laser desorption/ionization MS to hemolymph samples from individual flies before and after an immune challenge. This method provided precise information on the molecular masses of immune-induced molecules and allowed the detection, in the molecular range of 1.5-11 kDa, of 24 Drosophila immune-induced molecules (DIMs). These molecules are all peptides, and four correspond to already characterized antimicrobial peptides. We have further analyzed the induction of the various peptides by immune challenge in wild-type flies and in mutants with a compromised antimicrobial response. We also describe a methodology combining matrix-assisted laser desorption ionization time-of-flight MS, HPLC, and Edman degradation, which yielded the peptide sequence of three of the DIMs. Finally, molecular cloning and Northern blot analyses revealed that one of the DIMs is produced as a prepropeptide and is inducible on a bacterial challenge.

S-Sulfohemoglobin and disulfide exchange: the mechanisms of sulfide binding by Riftia pachyptila hemoglobins

The deep sea hydrothermal tube worm Riftia pachyptila possesses a multihemoglobin system with three different extracellular hemoglobins (Hbs; V1, V2, and C1): two dissolved in the vascular blood, V1 and V2, and one in the coelomic fluid, C1. V1 consists of four heme-containing chains and four linker chains. The globin chains making up V2 and C1 are, with one exception, common to V1. Remarkably these Hbs are able to bind oxygen and sulfide simultaneously and reversibly at two different sites. Two of the globin chains found in these three Riftia Hbs possess one free Cys residue and for at least one of the globins, the b-Cys75 is conserved among vestimentifera (Lamellibrachia sp.) and pogonophora (Oligobrachia mashikoi). By selectively blocking the free Cys with N-ethylmaleimide and using electrospray ionization mass spectrometry experiments, we show that these Cys residues are involved in sulfide binding by Riftia Hbs. Moreover, we also demonstrate that the larger V1 Hb can form persulfide groups on its linker chains, a mechanism that can account for the higher sulfide-binding potential of this Hb.

Penaeidins, a new family of antimicrobial peptides isolated from the shrimp Penaeus vannamei (Decapoda)

We report here the isolation of three members of a new family of antimicrobial peptides from the hemolymph of shrimps Penaeus vannamei in which immune response has not been experimentally induced. The three molecules display antimicrobial activity against fungi and bacteria with a predominant activity against Gram-positive bacteria. The complete sequences of these peptides were determined by a combination of enzymatic cleavages, Edman degradation, mass spectrometry, and cDNA cloning using a hemocyte cDNA library. The mature molecules (50 and 62 residues) are characterized by an NH2-terminal domain rich in proline residues and a COOH-terminal domain containing three intramolecular disulfide bridges. One of these molecules is post-translationally modified by a pyroglutamic acid at the first position. Comparison of the data obtained from the cDNA clones and mass spectrometry showed that two of these peptides are probably COOH-terminally amidated by elimination of a glycine residue. These molecules with no evident homology to other hitherto described antimicrobial peptides were named penaeidins.

Phosphorylation and O-glycosylation sites of bovine chromogranin A from adrenal medullary chromaffin granules and their relationship with biological activities

Bovine adrenal medullary chromogranin A, the major soluble component of chromaffin granules, is a phosphorylated glycoprotein. In the present work, phosphorylation and glycosylation sites were determined using mild proteolysis, peptide separation, microsequencing, and mass analysis by electrospray and matrix-assisted laser desorption ionization time-of-flight techniques. Seven post-translational modification sites were detected. Two O-linked glycosylation sites, each consisting of the trisaccharide NeuAcalpha2-3Galbeta1-3GalNAcalpha1, were located in the middle part of the protein, on Ser186 and on Thr231. The former residue is present in the antibacterial peptide named chromacin. Four phosphorylation sites were located on serine residues at positions Ser81 in the N-terminal region of the protein and Ser307, Ser372, and Ser376 in the C-terminal end. One additional phosphorylation site was found on the tyrosine residue at position Tyr173, the N-terminal amino acid of chromacin. With the exception of the phosphorylation on Tyr173, all of the other post-translational modifications are located on highly conserved chromogranin A regions, implying some biological importance.

Specific proteolytic cleavage of the myristoylated alanine-rich C kinase substrate between Asn 147 and Glu 148 also occurs in brain

The myristoylated alanine-rich C kinase substrate (MARCKS) is a major ubiquitous substrate of protein kinase C. The expression of the protein is regulated during cell cycle progression and cell proliferation. Specific proteolytic cleavage of the protein between Asn 147 and Glu 148 was described recently in cultured cells, and the corresponding proteolytic activity was observed in various tissue extracts except for brain. We purified a 40 kDa fragment of MARCKS from bovine brain that we characterized as the C-terminal specific fragment found in other tissues. The identification of the fragment was achieved by in vitro phosphorylation by protein kinase C, calcium-dependent interaction with calmodulin, mass spectrometric analysis, and N-terminal sequencing. These data suggest that specific proteolytic cleavage of MARCKS also occurs in brain and may be a general mechanism of down-regulation of the protein.

Gene cloning of rat and mouse platelet glycoprotein V: identification of megakaryocyte-specific promoters and demonstration of functional thrombin cleavage

Platelet glycoprotein (GP) V is a major surface protein cleaved during thrombin-induced platelet activation. GPV associates noncovalently with the GPIb-IX complex to form GPIb-V-IX, a receptor for von Willebrand factor and thrombin. We describe the cloning of the genes coding for rat and mouse GPV and compare them with the human gene. The two rodent genes have a similar structure and resemble the human GPV gene with a coding sequence (approximately 1,700 nucleotides) entirely contained in one exon and a single intron (approximately 900 nucleotides) in the 5' untranslated region. Both genes have megakaryocyte-type promoters with conserved tandem Ets and GATA recognition motifs and lack a TATA box. The mature rat and mouse proteins comprise 551 amino acids, have 70% sequence identity, and contain an additional 8-amino acid intracellular segment as compared with the human protein. As in human GPV, there is an NH2-terminal leucine-rich region of 15 repeats and a thrombin cleavage recognition sequence. Whereas the rat and human thrombin cleavage sites are similar, the mouse cleavage site resembles that of the human thrombin receptor. Functionality of these sites was demonstrated by thrombin cleavage of synthetic peptides and analysis by high-performance liquid chromatography (HPLC) or mass spectrometry. Cleavage of native rat GPV was confirmed by means of a polyclonal antibody directed against the new NH2-terminal peptide exposed after thrombin cleavage. This antibody specifically recognized thrombin-activated rat platelets by fluorescence-activated cell sorting (FACS) analysis. In addition, we raised monoclonal antibodies specific for rat GPV (88 kD), which recognized the NH2-terminal soluble fragment (70 kD) liberated after thrombin cleavage. Knowledge of these rodent GPV genes and availability of species-specific peptides and antibodies will be essential to further studies aiming to define the exact in vivo function of platelet GPV using animal models of thrombosis and gene inactivation experiments.

Addition of acetaldehyde to the N-terminus of a recombinant Schistosoma mansoni glutathione S-transferase upon high-level expression in Saccharomyces cerevisiae

Intracellular expression of recombinant Schistosoma mansoni protein p28 (Smp28) in soluble form to a concentration of more than 6 g/l culture in Saccharomyces cerevisiae was accompanied by a post-translational modification, which occurred during the late stage of the culture. The modified protein, which had a reduced isoelectric point, was isolated by anion-exchange HPLC and characterized by tryptic mapping by means of on-line reversed-phase HPLC/electrospray mass spectrometry. Comparison with non-modified recombinant Smp28 allowed us to localize the modification to the N-terminal hexapeptide AGEHIK, which had an increased mass of 26 Da. Reversed-phase HPLC of the modified peptide with a shallow acetonitrile gradient revealed the presence of two components of identical mass and amino acid composition. Both peptides were inaccessible to N-terminal Edman sequencing, indicating that a rearrangement of the N-terminal region of recombinant Smp28 had taken place during tryptic digestion leading to two isomeric, N-terminally blocked peptides. Deuterium-exchange mass spectrometry showed that the modified peptides lacked two exchangeable protons, suggesting cyclic modifications implying the N-terminal amino group. Tandem mass spectrometry by means of the nano-electrospray technique and collision-induced dissociation allowed us to identify the modified sites as Ala1, His4 and Lys6 based on a characteristic modified a1 ion of Ala1 (70.0 Da), a modified immonium ion of His4 (136.0 Da) and a modified y1" ion (173.2 Da) of Lys6. Combination of all the above results led to the conclusion that recombinant Smp28 was initially modified at its N-terminus by addition of acetaldehyde to form an aldimine which rearranged during tryptic digestion to two different cyclic peptides.