Effects of peptide hydrophobicity and charge state on molecular ion yields in plasma desorption mass spectrometry

High-through identification of T cell-specific phage-exposed mimotopes using PBMCs from tegumentary leishmaniasis patients and their use as vaccine candidates against Leishmania amazonensis infection

In the current study, phage-exposed mimotopes as targets against tegumentary leishmaniasis (TL) were selected by means of bio-panning cycles employing sera of TL patients and healthy subjects, besides the immune stimulation of peripheral blood mononuclear cells (PBMCs) collected from untreated and treated TL patients and healthy subjects. The clones were evaluated regarding their specific interferon-γ (IFN-γ) and interleukin-4 (IL-4) production in the in vitro cultures, and selectivity and specificity values were calculated, and those presenting the best results were selected for the in vivo experiments. Two clones, namely A4 and A8, were identified and used in immunization protocols from BALB/c mice to protect against Leishmania amazonensis infection. Results showed a polarized Th1 response generated after vaccination, being based on significantly higher levels of IFN-γ, IL-2, IL-12, tumour necrosis factor-α (TNF-α) and granulocyte-macrophage colony-stimulating factor (GM-CSF); which were associated with lower production of specific IL-4, IL-10 and immunoglobulin G1 (IgG1) antibodies. Vaccinated mice presented significant reductions in the parasite load in the infected tissue and distinct organs, when compared with controls. In conclusion, we presented a strategy to identify new mimotopes able to induce Th1 response in PBMCs from TL patients and healthy subjects, and that were successfully used to protect against L. amazonensis infection.

Cooperative effect of factors governing molecular ion yields in desorption/ionization mass spectrometry

Factors governing the molecular ion yields of amino acids and peptides have been studied using fast atom bombardment (FAB) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) in positive-ion mode. The ion yields of protonated amino acids under FAB conditions are dependent on proton affinity (PA), hydrophobicity, and aromaticity of amino acids. Both PA and hydrophobicity contribute to an increase in the ion yields, while aromaticity contributes to a decrease. In MALDI, the ion yields increase linearly with the increase of PA of amino acids with the exception of lysine. In both FAB and MALDI experiments with peptides, the presence of arginine residues is essential for producing abundant protonated peptides. In FAB, the presence of aliphatic and hydrophobic amino acids (leucine and isoleucine) increases the ion yields of protonated peptides, while some hydrophilic amino acids (aspartic acid and asparagines) decrease the ion yields. The presence of two or more arginine residues does not give higher ion yields in FAB. In MALDI, the presence of aromatic amino acids (phenylalanine and tyrosine) enhances the signals for protonated peptides. Thus, physicochemical factors of individual amino acids cooperatively affect the ion yields of protonated amino acids and peptides. These factors governing the ion yields in FAB and MALDI affect two processes, desorption and ionization, that can be considered independently.

The role of esterification on detection of protonated and deprotonated peptide ions in matrix assisted laser desorption/ionization (MALDI) mass spectrometry (MS)

Esterification was used to investigate how introduction of aliphatic chains within the peptide structure affects the MALDI response of ions analyzed in both polarity regimes. In binary mixtures containing equimolar amounts of a peptide with its correspondent alkyl ester, derivatization of the carboxylic groups has the tendency to increase MALDI detection of the modified protonated peptide ions. This positive effect on ion yield is more pronounced when longer alcohols are employed. In negative mode, the situation is antithetic and esterification produces a deleterious effect on the ion yield of the corresponding deprotonated species. From the data reported here we postulate that modifications of the acidic character of peptides prevent formation of anionic species under MALDI analysis. Furthermore, suppression of the formation pathway for anions alters the overall number of molecules which can undergo protonation. This results in an increased ion yield for the protonated esters.

Isolation and identification of intact chromogranin A and two N-terminal processing products, vasostatin I and II, from bovine adrenal medulla chromaffin granules by chromatographic and mass spectrometric methods

Chromogranin A (CGA) is the most abundant protein of the bovine adrenal medulla and plays an important role as precursor protein of several peptides that act as modulators for endocrine cell secretory activity. Furthermore, it is presumed to play a role in the targeting of peptide hormones and neurotransmitters to granules of the regulated pathway. However, its complete primary structure and proteolytic processing have not yet been identified. This study describes a rapid and efficient procedure for the high yield isolation of bovine CGA and its N-terminal processing products, vasostatin I and II. Using the lysate from bovine adrenal medulla chromaffin granules, the soluble proteins were purified by three consecutive HPLC steps, thereby avoiding the use of buffer solutions. The protein fractions were isolated and characterized by SDS-PAGE and Western blot analysis as well as by mass spectrometry. In the latter analysis, the efficiency of matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS) was demonstrated, enabling the unequivocal and sensitive characterization of proteins from crude mixtures. Sufficient amounts of pure protein were obtained by the present procedure to form the basis for detailed structural studies by spectroscopic methods and X-ray crystallography.