RESUMEN
The quantitative analysis of protein mixtures is pivotal for the understanding of variations in the proteome of living systems. Therefore, approaches have been recently devised that generally allow the relative quantitative analysis of peptides and proteins. Here we present proof of concept of the new metal-coded affinity tag (MeCAT) technique, which allowed the quantitative determination of peptides and proteins. A macrocyclic metal chelate complex (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)) loaded with different lanthanides (metal(III) ions) was the essential part of the tag. The combination of DOTA with an affinity anchor for purification and a reactive group for reaction with amino acids constituted a reagent that allowed quantification of peptides and proteins in an absolute fashion. For the quantitative determination, the tagged peptides and proteins were analyzed using flow injection inductively coupled plasma MS, a technique that allowed detection of metals with high precision and low detection limits. The metal chelate complexes were attached to the cysteine residues, and the course of the labeling reaction was followed using SDS-PAGE and MALDI-TOF MS, ESI MS, and inductively coupled plasma MS. To limit the width in isotopic signal spread and to increase the sensitivity for ESI analysis, we used the monoisotopic lanthanide macrocycle complexes. Peptides tagged with the reagent loaded with different metals coelute in liquid chromatography. In first applications with proteins, the calculated detection limit for bovine serum albumin for example was 110 amol, and we have used MeCAT to analyze proteins of the Sus scrofa eye lens as a model system. These data showed that MeCAT allowed quantification not only of peptides but also of proteins in an absolute fashion at low concentrations and in complex mixtures.
Asunto(s)
Compuestos Heterocíclicos con 1 Anillo/química , Elementos de la Serie de los Lantanoides/química , Péptidos/análisis , Proteínas/análisis , Proteómica/métodos , Secuencia de Aminoácidos , Animales , Bovinos , Quelantes/química , Cristalinas/análisis , Electroforesis en Gel de Poliacrilamida , Cristalino/química , Datos de Secuencia Molecular , Espectrometría de Masa por Ionización de Electrospray , Espectrometría de Masa por Láser de Matriz Asistida de Ionización Desorción , Sus scrofaRESUMEN
An approach for the identification of unknown selenium-containing biomolecules was developed, enabling the identification of selenodiglutathione (GS-Se-SG) and the mixed selenotrisulfide of glutathione and cysteinylglycine (GS-Se-SCG) in aqueous yeast extracts. The method consists of two-dimensional liquid chromatography, inductively coupled plasma mass spectrometry (ICPMS) and nanoelectrospray tandem mass spectrometry. Analytes were separated by size-exclusion chromatography followed by preconcentration and separation on a porous graphitic carbon HPLC column. The HPLC effluent was monitored for selenium by ICPMS, and two selenium-containing fractions were isolated and analyzed by nanoelectrospray MS. The nanoelectrospray technique has a low sample consumption of approximately 80 nL/min, enabling a preconcentration of the sample to a few microliters. Mass spectra of the two fractions showed the characteristic Se isotopic pattern centered at m/z 693.1 and 564.0 for the [M + H]+ 80Se ions. MS/MS spectra of adjacent parent ions confirmed the presence of Se. The two selenium species were identified as GS-Se-SG and GS-Se-SCG by collision induced dissociation (CID). The accurately measured masses of the most abundant 691 and 693 u parent ions are in good agreement (differences = 3 ppm) with the theoretical masses. To our knowledge, this is the first identification of GS-Se-SG and GS-Se-SCG in biological matrixes by MS/MS.
Asunto(s)
Cromatografía Líquida de Alta Presión/métodos , Dipéptidos/química , Glutatión/análogos & derivados , Glutatión/química , Espectrometría de Masas/métodos , Compuestos de Organoselenio/química , Saccharomyces cerevisiae/química , Compuestos de Selenio/química , Selenio/análisis , Sulfuros/químicaRESUMEN
An HPLC/MS-MS method was developed for the analysis of selenium species. Tandem mass spectrometry (MS-MS) was chosen as a detector to provide structural and molecular information allowing the identification of species, which are not commercially available as standards. A new separation method for selenium species was developed, based on porous graphitic carbon (PGC) as the stationary phase. The applicability of the optimized HPLC/MS-MS system was demonstrated by the analysis of a mixture containing Se-methyl-selenocysteine, selenomethionine, selenocystine, selenoethionine and selenocystamine. All peaks were baseline-resolved and eluted within 16 min. Positive ionization led to higher intensities than negative ionization. Signal suppression tests showed that electrospray ionization (ESI) is a more effective ionization method than atmospheric pressure chemical ionization (APCI) for selenium species in a matrix containing pentafluoropropionic acid, heptafluorobutyric acid or ammonium formate. Comparative experiments with a triple quadrupole mass spectrometer (Quattro LC) and a time-of-flight instrument (Q-Tof-2) showed a 20 fold higher mass resolution of the latter mass spectrometer (m/Am= 5000) and significantly lower intensities for analyte signals as well as background noise compared to the triple quadrupole instrument. MS-MS spectra of the investigated selenium species including characteristic fragmentation patterns are presented.