Mass spectrometric identification of in vivo carbamylation of the amino terminus of Ectothiorhodospira mobilis high-potential iron-sulfur protein, isozyme 1

The complete amino acid sequence of a novel high-potential iron-sulfur protein (HiPIP) isozyme 1 from the moderately halophilic phototrophic bacterium Ectothiorhodospira mobilis was determined by a combined approach of chemical and mass spectrometric sequencing techniques. By mass analysis of the apo- and holo-protein in the positive electrospray ionization mode using different electrospray solvents, the protein was found to be post-translationally modified by a moiety of 43 Da. Further analysis showed the nature and location of this modification to be a carbamyl group at the N-terminus of the HiPIP. This rare type of modification has previously been reported to occur in the water-soluble human lens alphaB-crystallin, class D beta-lactamases and some prokaryotic ureases, albeit at an internal lysine residue. In this paper, we discuss the mass spectrometric features of a carbamylated residue at the N-terminus of a peptide or a lysine side-chain during sequence analysis by collision-induced dissociation tandem mass spectrometry. Our data provide evidence for the first case of a prokaryotic carbamylated electron transport protein occurring in vivo.

Characterization of glutathione amide reductase from Chromatium gracile. Identification of a novel thiol peroxidase (Prx/Grx) fueled by glutathione amide redox cycling

Among the Chromatiaceae, the glutathione derivative gamma-l-glutamyl-l-cysteinylglycine amide, or glutathione amide, was reported to be present in facultative aerobic as well as in strictly anaerobic species. The gene (garB) encoding the central enzyme in glutathione amide cycling, glutathione amide reductase (GAR), has been isolated from Chromatium gracile, and its genomic organization has been examined. The garB gene is immediately preceded by an open reading frame encoding a novel 27.5-kDa chimeric enzyme composed of one N-terminal peroxiredoxin-like domain followed by a glutaredoxin-like C terminus. The 27.5-kDa enzyme was established in vitro to be a glutathione amide-dependent peroxidase, being the first example of a prokaryotic low molecular mass thiol-dependent peroxidase. Amino acid sequence alignment of GAR with the functionally homologous glutathione and trypanothione reductases emphasizes the conservation of the catalytically important redox-active disulfide and of regions involved in binding the FAD prosthetic group and the substrates glutathione amide disulfide and NADH. By establishing Michaelis constants of 97 and 13.2 microm for glutathione amide disulfide and NADH, respectively (in contrast to K(m) values of 6.9 mm for glutathione disulfide and 1.98 mm for NADPH), the exclusive substrate specificities of GAR have been documented. Specificity for the amidated disulfide cofactor partly can be explained by the substitution of Arg-37, shown by x-ray crystallographic data of the human glutathione reductase to hydrogen-bond one of the glutathione glycyl carboxylates, by the negatively charged Glu-21. On the other hand, the preference for the unusual electron donor, to some extent, has to rely on the substitution of the basic residues Arg-218, His-219, and Arg-224, which have been shown to interact in the human enzyme with the NADPH 2'-phosphate group, by Leu-197, Glu-198, and Phe-203. We suggest GAR to be the newest member of the class I flavoprotein disulfide reductase family of oxidoreductases.

Conformational variability of the synthetic peptide 129-141 of the mouse prion protein

The effect of solution conditions on the conformation of the peptide corresponding to residues 129-141 of the mouse prion protein has been examined by experimental and theoretical tools including circular dichroism, secondary structure predictions, and Molecular Dynamics simulations. The conformational properties of the peptide observed by CD confirm the prediction results: the peptide is chiefly random coil in water. The conformational sampling performed by Molecular Dynamics simulations in water also corroborates the flexibility of the peptide, in particular for the N-terminal part. We show, however, that the peptide samples hairpin conformations in one of several approximately 1-ns Molecular Dynamics simulations in water. Interestingly, the analysis of the CD spectra obtained in this study suggests the presence of beta-structure which, given the length of the peptide, can only consist in beta-hairpin. The peptide can also be induced to form a modest percentage of helical structure in the presence of organic cosolvents such as trifluoroethanol, or detergents such as sodium dodecyl sulfate and lysophosphatidylcholine. This result is different from that obtained for a homologous hamster fragment, which differs from the mouse sequence by the single substitution of Ile 139 to Met. Interestingly, this substitution is crucial for the barrier in the transmission of the prion disease between hamsters and mice.

SODs are involved in the regulation of ICAM-1 expression in human melanoma and endothelial cells

It is well known that ICAM-1 expression can be stimulated by TNF and by oxidative stress, via the activation of specific transcription factors. Two of these--NFkappaB and AP-1--can also be activated by reactive oxygen species, including the superoxide anion (also produced under TNF challenge). The latter is inactivated by superoxide dismutase of which two forms exist: Cu/Zn-SOD (cytoplasmic) and Mn-SOD (mitochondrial). We investigated whether superoxide anion direct generation or accumulation through specific SOD inhibition, may affect ICAM-1 expression in human melanoma and endothelial cells. Our results show a 20-50% increase in both SOD activities when cells were exposed to TNF or to an oxidative stress produced by Paraquat (a generator of superoxide anion radicals), both in terms of enzymes activity (zymogram) and protein levels (Western blotting and ELISA). Either with TNF or Paraquat, we could measure a significant increase of ICAM-1 expression with maxima ranging from 140 to 200%, depending on the cell line. Specific inhibition of Cu/Zn-SOD activity by DTIC (diethyldithiocarbamic acid), in presence of Paraquat or TNF, was followed by an upregulation of ICAM-1 expression (60 and 20%, respectively). In contrast, the addition of a SOD mimetic (MnTMPyP) completely inhibited Paraquat-stimulated ICAM-1 expression in melanoma cells and significantly decreased it in HUVEC (50%). In presence of TNF however, the same SOD mimetic inhibited TNF-stimulated ICAM-1 expression by 25% in melanoma and 17% in endothelial cells. In conclusion, these data provide evidence that melanoma and endothelial cells exposure to TNF or oxidative stress results in a significant increase of both Mn- and Cu/Zn-SOD activities. This increase seems to be associated with a reduction in the stimulation of ICAM-1 expression by TNF or oxidative stress.

Electrospray mass spectrometric analysis of new alpha-MSH analogues carrying nitrogen mustard at their amino terminus

Two different chlorinated drugs, chlorambucil and melphalan, have been linked to the carrier alpha-melanocyte-stimulating hormone at the end of the solid-phase peptide synthesis of the hormone. The [Nle4, D-Phe7] and the [Nle4, L-Phe7] derivatives of the hormone have both been used. It was found by electrospray mass spectrometric analysis that the products undergo hydrolysis of the chlorinated moiety of the drugs, most likely due to the acidic conditions necessary for cleavage of the peptide from the resin. Only the melphalan-O(ethyl)-N(succinyl)-derivative of alpha-melanocyte-stimulating hormone [Nle4, L-Phe7] did not show a bis-hydroxylated form. It was proven by blank experiments with commercially available melphalan that this mustard occurs for some 45%-50% in the mono-hydroxylated form, which is known to be pharmacologically poorly active.

[Hemisynthesis of antineoplastic conjugates with nitrogen-mustard proteins]

The synthesis of new conjugates with inhibitory action on tumour growth is investigated by linking amino functions of proteins compounds (lysozyme and alpha s-casein) through an amide linkage at the carboxylic function of nitrogen mustards (chlorambucil and melphalan). The polychlorambucil amides of lysozyme and alpha s-casein derivatives prepared showed experimental antitumour activity when these conjugates were screened against the experimental P388 leukemia. In the case of the conjugates lysozyme-melphalan, an antitumour activity is observed when the amino function of the drug is combined with the carboxylic functions of the protein contrary to the situation of the free amino function of the drug described into the literature.

[Reaction of carbodiimide for the introduction of p-bis(2-chloroethyl)amino-L-phenylalanine to lysozyme]

In the synthesis of new prodrugs with inhibitoring action of tumour growth, a new nitrogen mustard derivative was obtained, proceeding of the coupling between an egg-white lysozyme with an antitumor amine nucleophile, the methyl ester of p-bis-(2-chloroethyl)amino-L-phenylalanine (Melphalan), catalyzed by 1-ethyl-3-[3-(dimethylamino)propyl] carbodiimide (EDC), at pH 5.0 and room temperature. In that case, the mechanism for the modification isn't selective of Asp101 in lysozyme. As in cases of histamine and D-glucosamine [3], it is evident that Melphalan is one type of amine who doesn't cause a selective modification of Asp101 but causes somewhat random reaction, because Asp101 is modified followed by modifications of other carboxyls. In this case, we suggest that the amine (Melphalan) may also bind to the substrate binding site in competition with EDC. With this type of amine, enzyme-nucleophile interactions predominate, and the selective activation of Asp101 by EDC is reduced to lead a more random reaction.

[Carbon 13 nuclear magnetic resonance conformation studies of peptides with analgesic activity]

13C Nuclear magnetic resonance studies of proline peptides with central antalgic activity (Pro-Arg, Arg-Pro, Pro-Arg-Pro, Pro-Lys-Pro) indicate a predominance of trans conformation at all pH values; but their physiological activities appear to be related to the ability of the C-terminal proline peptides to assume the cis conformation.