Second harmonic generation from tryptophan-rich short peptides: W(n)K(m) and gramicidin A.

We report the first hyperpolarizability of a series of tryptophan-rich short peptides with the respective sequence KWK, KWWK, KWWWK, KWWKWWK, where W and K stand for tryptophan and lysine. The measurements were performed with the technique of hyper-Rayleigh scattering in the bulk of an aqueous Tris buffer solution at a pH of 8.5 and a salt concentration of 150 mM at the non-resonant fundamental wavelength of 784 nm. The first hyperpolarizability of the different peptides follows a simple additive model scaling with the number of tryptophan residues contained in the peptide. However, it appears that the first hyperpolarizability response of a single tryptophan residue in the peptide strongly differs from that of an isolated tryptophan. Hence, it is therefore demonstrated that the local environment of the tryptophan residues within the peptide strongly influences its nonlinear optical response. A comparison with the first hyperpolarizability of the natural peptide gramicidin A measured in trifluoroethanol (TFE) further confirms the key role of the local environment on the first hyperpolarizability of tryptophan residues in peptides.

First hyperpolarizability of the natural aromatic amino acids tryptophan, tyrosine, and phenylalanine and the tripeptide lysine-tryptophan-lysine determined by hyper-Rayleigh scattering.

We report the first hyperpolarizability of tryptophan (Trp) and tyrosine (Tyr) and an upper limit for that of phenylalanine (Phe), three natural aromatic amino acids. The measurements were performed with hyper-Rayleigh scattering in an aqueous Tris buffer solution at a pH of 8.5 and 150 mM salt concentration with a fundamental wavelength of 780 nm. A value of (4.7 ± 0.7) × 10(-30) esu is found for Trp and (4.1 ± 0.7) × 10(-30) esu for Tyr whereas the upper limit of 1.4 × 10(-30) esu is found for that of Phe due to its limited solubility. The influence of the presence of lysine (Lys) in close vicinity of Trp is investigated with a measurement of the first hyperpolarizabilty of Trp in an excess of Lys and compared to the first hyperpolarizability obtained for the tripeptide Lys-Trp-Lys. The clear decrease of the values measured in these two cases indicates that the first hyperpolarizabilty of Trp is very sensitive to its local environment.

Ca(2+)-induced changes of surfactin conformation: a FTIR and circular dichroism study.

Previous NMR studies on surfactin proposed two gamma or beta-turn-containing conformers while recent CD studies described beta-sheets and alpha-helices in surfactin. Since these data were not obtained in the same conditions, the conformation of surfactin was reinvestigated by FTIR spectroscopy, a diagnostic method for beta-sheets. In trifluoroethanol, the FTIR spectra of surfactin and its diester are compatible with gamma and/or beta-turn(s) and the differences in their CD spectra show the importance of the Glu(1) and Asp(5) COOH groups in stabilizing the lipopeptide conformation. The calcium-induced spectral changes of both lipopeptides suggest a first binding of the divalent ions to the surfactin COOH groups (until calcium-lipopeptide mole ratio reached 1) followed by bulk conformational changes (at higher mole ratios). In Tris buffer at pH 8.5, the FTIR amide I band shape, without the typical 1610-1628 and 1675-1695 cm(-1) bands, ascertains the absence of beta-sheets.

NMR structure of antibiotics plipastatins A and B from Bacillus subtilis inhibitors of phospholipase A(2).

Plipastatins A and B are antifungal antibiotics belonging to a family of lipopeptides capable of inhibiting phospholipase A(2) (PLA(2)) and are biosynthesised under certain circumstances by Bacillus subtilis. U-(15)N plipastatins A and B were obtained from cultures of the strain NCIB 8872 on a Landy medium modified for stable-isotope labelling by the substitution of the L-glutamic acid used as the sole nitrogen source, by (15)NH(4)Cl. These two lipo-decapeptides, lactonised by esterification of the Ile10 C-terminus with the phenolic hydroxyl of Tyr3, differ only by a D-Ala (plipastatin A)/D-Val (plipastatin B) substitution at the position 6. The (1)H- and (15)N-nuclear magnetic resonance (NMR) signals of a 4:6 mixture of plipastatins A and B were unambiguously assigned and their structures in dimethylsulfoxide solution were calculated on the basis of a set of NMR-derived restraints. Plipastatins A and B are well-defined structures in solution stabilised by a type 1 beta-turn comprising residues 6-9 and several other specific hydrogen bonds. The structures afford a first molecular basis for the future studies of their biological activities both in lipidic layers or on PLA(2).

Role of metal ions on the secondary and quaternary structure of alkaline phosphatase from bovine intestinal mucosa.

Alkaline phosphatase (EC 3.1.3.1) from bovine intestinal mucosa (BIAP) is an homodimeric metalloenzyme, containing one Mg2+ and two Zn2+ ions in each active site. ApoBIAP, prepared using ion-chelating agents, exhibited a dramatic decrease of its hydrolase activity, concomittant to conformational changes in its quaternary structure. By rate-zonal centrifugation and electrophoresis, we demonstrated, for the first time, that the loss of divalent ions leads to some monomerization process for a metal-depleted alkaline phosphatase. Divalent ions are also involved in the secondary and tertiary structures. Metal-depletion induced more exposure of some Trp residues and hydrophobic regions to the solvent (as proved by intrinsic and ANS fluorescences). These changes might correspond to the disappearance of alpha-helices and/or turns with a concomittant appearance of unordered structures and beta-sheets (as probed by FTIR spectroscopy). For BIAP, three steps of temperature-induced changes were exhibited, while for apoBIAP, only one step was exhibited at 55 degrees C. Our work on BIAP showed two main differences with alkaline phosphatase from Escherichia coli. The loss of the divalent ions induces protein monomerization and the total recovery of enzyme activity by divalent ion addition to apoBIAP was not obtained.

NMR structure of active and inactive forms of the sterol-dependent antifungal antibiotic bacillomycin L.

The antifungal antibiotic lipopeptide bacillomycin L [cyclo-(L-Asp1-D-Tyr2-D-Asn3-L-Ser4-L-Gln5-D-Ser6++ +-L-Thr7-beta-amino fatty acid)] from Bacillus subtilis belongs to the iturinic family of antifungal agents and acts with a strict sterol-phospholipid dependence on biomembranes. This antibiotic has been analysed using solution NMR spectroscopy in its native active form and its inactive (L-Asp1, D-Tyr2) di-O-methylated form. The structures were calculated under NMR-derived restraints using molecular-dynamic simulated-annealing protocols starting from a random array of atoms. The structure of the native antibiotic is spread over different conformers in which two families are recognized. It was found that most structures have dihedral phi and psi angles defining a type-II' beta-turn including amino acids 5-8, in certain cases stabilized by a 8HN-5CO hydrogen bond, whereas a minority of structures adopt an inverse gamma-turn including amino acids 6-8, stabilized in all cases by an 8HN-6CO hydrogen bond. The di-O-methylation of L-Asp1 and D-Tyr2, an amino acid strictly conserved within the iturinic group of antibiotics, does not induce major differences in the NMR spectra and in the NMR structures. The results are discussed in relation to the specific loss of interaction with sterols when the native antifungal bacillomycin L is methylated on the conserved D-Tyr2 position.

A FTIR spectroscopy evidence of the interactions between wheat germ agglutinin and N-acetylglucosamine residues.

Wheat germ agglutinin (WGA), a lectin binding a N-acetyl-D-neuraminic acid (NeuNAc) and/or N-acetyl-D-glucosamine (GlcNAc) group, was studied by Fourier transform infrared (FTIR) spectroscopy. Deconvolution of the FTIR spectrum of WGA alone indicated the presence of few alpha-helices and beta-sheets, in contrast to many other lectins. These results agree with previous WGA crystal data. The WGA conformational changes, induced by GlcNAc-bearing liposomes or GlcNAc oligomers, were studied by infrared differential spectroscopy. The GlcNAc binding to WGA resulted in a decrease of turns and alpha-helices and a concomitant appearance of beta-sheets, inducing more or less peptidic N-H deuteration.

Conformational changes of arginine kinase induced by photochemical release of nucleotides from caged nucleotides--an infrared difference-spectroscopy investigation.

The conformations of arginine kinase (AK) in AK x Mg x ADP, AK x Mg x ATP, AK x Mg x ADP x NO3-, AK x Mg x ADP x Arg and AK x Mg x ADP x NO3- x Arg complexes were investigated by measuring their reaction-induced infrared difference spectra (RIDS). The photochemical release of ATP from ATP[Et(PhNO2)] and of ADP from ADP[Et(PhNO2)] produced distinct RIDS of AK complexes, suggesting that binding of ADP and ATP promoted different structural alterations of the enzyme active-site. Small infrared changes in the amide-I region were observed, indicating that about 5-10 amino acid residues were involved in the nucleotide-binding site. These infrared changes were due to the structural alteration of the peptide backbone caused by the nucleotide-binding and to the coupling effects between the nucleotide-binding site and the other substrate (Arg or NO3-)-binding site. ATP binding to AK (as well as ADP-binding to AK in the presence of NO3-) induced protonation of a carboxylate group of Asp or Glu, as evidenced by the appearance of the 1733-cm(-1) band, which was not observed with the AK x Mg x ADP, AK x Mg x ADP x Arg and AK x Mg x ADP x NO3- x Arg complexes. The RIDS of the AK x Mg x ADP x NO3- x Arg complex showed new infrared bands at 1622 cm(-1) (negative) and at 1613 cm(-1) (positive), which were not seen in the RIDS of other complexes (without NO3- or/and Arg). In the transition-state-analog complex of AK, no protonation of the carboxylate residue (Asp or Glu) was observed, and the binding site of NO3- or the gamma-phosphate group of nucleotide was altered.

[Results of a randomized study comparing combination of navelbine-cisplatin to combination of vindesine-cisplatin and to navelbine alone in 612 patients with inoperable non-small cell lung cancer]. / Résultats d'une étude randomisée comparant l'association Navelbine-cisplatinum à l'association vindésine-cisplatinum et à la Navelbine seule chez 612 malades porteurs d'un carcinome bronchique non à petites cellules inopérable.

The combination of vindesine and cisplatin is considered a reference regimen in advanced NSCLC which has yielded a significant improvement in the duration of survival. A phase II study of a new semi-synthetic vinca alkaloid, Navelbine, reported an unusually high 29% response rate in stage III-IV NSCLC and a phase I-II study established the feasibility of the combination of Navelbine and cisplatin. We, therefore, designed a prospective randomized trial to compare Navelbine and cisplatin (NVB-P) to vindesine and cisplatin (VDS-P) and to evaluate whether the best of these regimens affords a survival benefit compared to Navelbine alone (NVB), an outpatient regimen. Forty-five centers included 612 patients in this study: 206 in NVB-P, 200 in VDS-P and 206 in NVB. Navelbine was given at a dose of 30 mg/m2 weekly, cisplatin at 120 mg/m2 on day 1, day 29 and then every 6 weeks and vindesine at 3 mg/m2 weekly for 6 weeks and then every other week. Treatment was continued until progression or toxicity. Patients' characteristics were similar in the three groups with 59% of patients presenting with metastatic disease. An objective response rate was observed in 30% of patients in NVB-P versus 19% in VDS-P (P = .02) and 14% in NVB (P < .001). The median duration of survival was 40 weeks in NVB-P compared to 32 weeks in VDS-P and 31 weeks in NVB. The comparison of survival between the three groups demonstrated an advantage for NVB-P compared to VDS-P (P = .04) and NVB (P = .02). Neutropenia was significantly higher in the NVB-P group (P < .001) and neurotoxicity more frequent with VDS-P (P < .004). Since our results have demonstrated that NVB-P yields a longer survival duration and a higher response rate than VDS-P or NVB alone, with acceptable toxicity, this combination should be considered a reference regimen in advanced NSCLC.

Inhibition of gap junction intercellular communications of cultured rat hepatocytes by ethanol: role of ethanol metabolism.

BACKGROUND/AIMS: In a previous study, we reported that in cultured rat hepatocytes, ethanol inhibits intercellular communication which is known to play a central role in the regulation of cell growth and differentiation. This work was designed to find out if ethanol exerts a direct action on cell membranes, comparable to other long-chain (C6-C9) alcohols, or an indirect action. METHODS: Intercellular communication was measured on short-term cultured rat hepatocytes by the fluorescent Lucifer-Yellow CH transfer method. Intracellular pH was measured by spectrofluorimetry and membrane expression of connexin 32 by indirect immunofluorescence. RESULTS: Under our conditions, ethanol (20 mM) inhibited intercellular communication of hepatocytes to the same extent as did octanol and 1 mM. Immunofluorescence semi-quantitative studies of connexin 32 suggested that the observed inhibition was not related to a decrease in the number of gap junction plaques. In contrast with those of octanol, the inhibitory effects of ethanol appeared to be indirect because the inhibition of ethanol metabolism by 4-methyl pyrazole abolished its effects on intercellular communication, while 4-methyl pyrazole did not influence the effects of octanol. Acetaldehyde, the main metabolite of ethanol was without effect on gap junctions. CONCLUSIONS: This suggests that the inhibition of intercellular communication induced by ethanol may be included among the consequences of intermediary cell metabolism disturbances indirectly due to ethanol oxidation. This may be one of the mechanisms by which ethanol metabolism exerts a hepatotoxic possibly carcinogenic action.

Characterization of iturin synthetase in the wild-type Bacillus subtilis strain producing iturin and in an iturin deficient mutant.

The multi-enzyme system responsible for the biosynthesis of iturin, an antifungal lipopeptide of Bacillus subtilis, was partially purified by chromatography on different affigels. In the wild-type strain, two subunits of the iturin synthetase (ITs and ITagp) were characterized: ITs activated only L-Ser, one of the iturin amino acid components, and ITagp activated L-Asn, D-Asn, L-Gln and L-Pro, amino acids corresponding to a partial sequence of iturin. In an iturin deficient mutant, the activity of the ITagp subunit was modified.

Studies on lipopeptide biosynthesis by Bacillus subtilis: isolation and characterization of iturin-, surfactin+ mutants.

Two mutant strains, M35 and M89, were obtained by UV irradiation from a wild-type Bacillus subtilis producing iturin and surfactin. Sporulation and surfactin production were similar in both mutants and in the parent strain, while the iturin production of M35 was 300-fold less than that of the wild-type strain; M89 did not produce any iturin. The analysis of the incorporation of sodium [1-14C]acetate into cellular lipids and lipopeptides showed that M89 still synthesized beta-amino fatty acids, the lipid moiety of iturin.

A three-arm trial of vinorelbine (Navelbine) plus cisplatin, vindesine plus cisplatin, and single-agent vinorelbine in the treatment of non-small cell lung cancer: an expanded analysis.

Phase II studies have demonstrated that vinorelbine (Navelbine; Burroughs Wellcome Co, Research Triangle Park, NC; Pierre Fabre Médicament, Paris, France) alone or in combination with cisplatin has promising activity against non-small cell lung cancer (NSCLC). On the basis of these preliminary trials, a phase III study was designed to compare intravenous vinorelbine (30 mg/m2 weekly) plus cisplatin (120 mg/m2 on day 1 and day 29 and then every 6 weeks) with vindesine (3 mg/m2 weekly for 6 weeks and then every 2 weeks) plus cisplatin, and to evaluate whether the best of these regimens afforded a survival benefit compared with intravenous vinorelbine alone, an outpatient regimen. This report presents an expanded analysis of data from this previously published study. Six hundred twelve patients were enrolled in this trial: 206 in the vinorelbine plus cisplatin arm, 200 in the vindesine plus cisplatin group, and 206 in the single-agent vinorelbine arm. The vinorelbine plus cisplatin regimen was superior to the other two arms of the study in objective response rate (30% v 19% for vindesine plus cisplatin [P = .02] and 14% for vinorelbine alone [P = .001]), median survival duration (40 weeks v 32 weeks for vindesine plus cisplatin and 31 weeks for vinorelbine alone), and 1-year survival rate (35% v 27% for vindesine plus cisplatin and 30% for vinorelbine alone). An adjusted log-rank test provided a significant advantage for vinorelbine plus cisplatin when compared with vindesine plus cisplatin (P = .04) and with vinorelbine alone (P = .02). The major difference in survival between the two cisplatin-containing regimens occurred in patients with metastatic (stage IV) NSCLC. The incidence of granulocytopenia was significantly higher in the vinorelbine plus cisplatin arm compared with the other two treatment groups, but neurotoxicity was significantly more frequent in the vindesine plus cisplatin group. The results of this study indicate that the combination of vinorelbine plus cisplatin is a viable treatment option for patients with NSCLC and may provide advantages compared with other commonly used regimens.

Studies on bacillomycin D biosynthesis by Bacillus subtilis.

The biosynthesis of bacillomycin D, an antibiotic containing a beta-amino fatty acid and a peptide moiety with asparagine, glutamic acid, serine, proline, threonine, and tyrosine, was studied by incubating the Bacillus subtilis producer with various 14C-labelled precursors. Sodium acetate was incorporated into beta-amino fatty acids of bacillomycin D, and asparagine was the best precursor of the peptidic moiety. The kinetics of the incorporation of radioactive substrates into bacillomycin D and into beta-amino fatty acids show that the lipid and the peptide moieties of the antibiotic were synthesized at the same stage of growth of the bacteria. Comparing the effects of different inhibitors on the incorporation of radioactive precursors, the bacillomycin D and beta-amino fatty acids biosyntheses are discussed in relation to the biosyntheses of proteins, lipids and with sporulation.

Biosynthesis of bacillomycin D by Bacillus subtilis. Evidence for amino acid-activating enzymes by the use of affinity chromatography.

Bacillomycin D is an antifungal lipopeptide produced by B. subtilis. The formation of the peptidyl bonds of bacillomycin D occurs non-ribosomally, as demonstrated by the use of chloramphenicol, an inhibitor of protein biosynthesis. Amino acid-activating enzymes were found in B. subtilis cell lysates purified by affinity chromatography on a gel containing L-Pro, an amino acid of bacillomycin D. Presence of ATP during this purification increases the binding of enzymatic proteins and their activity. An enzyme, with an apparent molecular weight of 230 kDa, catalyzed ATP-PPi exchange reactions, which were mediated by specific amino acids, corresponding to a partial sequence of bacillomycin D.

Phase I-II study of vinorelbine (Navelbine) plus cisplatin in advanced non-small cell lung cancer.

32 patients with advanced non-small cell lung cancer previously untreated by chemotherapy were included in a phase I-II study in order to determine the feasibility of the combination of vinorelbine and cisplatin, each administered at its optimal dose, i.e. 30 mg/m2 weekly and 120 mg/m2 every 4-6 weeks, respectively. There were 27 males and 5 females with a mean age of 55 years and a median performance status of 80%. 13 had locally advanced disease and 19 had distant metastases at the time of inclusion. Our study demonstrated the feasibility of this protocol. Dose intensities could be maximised by adapting vinorelbine doses rather than by postponing treatment in the event of neutropenia. Both response rate (33%) and overall survival of the population (median 11 months) justify further studies.

Synthesis of beta-hydroxy fatty acids and beta-amino fatty acids by the strains of Bacillus subtilis producing iturinic antibiotics.

The iturinic antibiotics, which contain long chain beta-amino acids, are produced by Bacillus subtilis. Screening these strains for the presence of a possible precursor of the iturinic antibiotics, we isolated a lipopeptide containing beta-hydroxy fatty acids. The structure of this compound was studied and it appears to be identical or structurally very similar to surfactin. The carbon chain of its beta-hydroxy fatty acids was n C16, iso C16, iso C15 or anteiso C15. The percentages of each beta-hydroxy fatty acids varied according to the strain producing iturinic antibiotics and were influenced by addition of branched-chain alpha-amino acids to the culture medium. These results demonstrate for the first time that iso C14 beta-hydroxy fatty acid is a constituent present in such a surfactin like lipopeptide. Besides, the presence of radioactive beta-hydroxy fatty acids in the phospholipids when the strains were grown in the presence of sodium [14C]acetate seems also characterize the different strains producing iturinic antibiotics.

Influence of divalent ions on the solubility of iturin and bacillomycin L, antifungal peptidolipids of Bacillus subtilis.

When calcium chloride was added to the culture medium of strains producing iturin or bacillomycin L, the antibiotic, normally excreted in the supernatant of the culture medium, was found in the cell pellet. This apparent inhibition of the antibiotic excretion was studied and it was demonstrated that CaCl2 precipitated the antibiotic after its excretion in the medium. The ability of various chloride salts to precipitate iturin and bacillomycin L was tested and the most effective salts were CaCl2 and MnCl2. Comparison of the compounds obtained by CaCl2 precipitation and by acid precipitation showed that, in the latter case, major antibiotics were accompanied by minor congeners resulting from modifications of genuine antibiotics.

Studies on the antifungal antibiotics: bacillomycin D and bacillomycin D methylester.

Bacillomycin D, an antifungal compound of Bacillus subtilis, was produced during the stationary phase of growth when all the glucose of the medium was exhausted and the pH reached about 8. In addition to bacillomycin D, bacillomycin D methylester was characterized by its antifungal properties and its haemolytic activity.