No abstract

We studied the natural MHC class I display of measles virus (MV) epitopes. Peptide ligands associated with HLA‐A*0201 were purified from a B lymphoblastoid cell line prior to and after infection with MV. Infection‐induced peptides were revealed using microcapillary reversed phase high performance liquid chromatography electrospray ionization / mass spectrometry (μLC‐ESI / MS) by subtraction of the "infected" and "uninfected" ion traces. Three naturally processed viral epitopes derived from different MV proteins were identified through tandem MS sequencing. These peptides were expressed at widely divergent levels of HLA‐peptide complexes, but had similar binding capacities to HLA‐A*0201. The most abundant viral peptide species, identified as residues 84 – 92 (KLWESPQEI) of the MV nonstructural C protein, was expressed at an unprecedented high density (> 105 copies per cell) and was immunogenic in HLA‐A2 / Kb‐transgenic mice. Furthermore, natural mutants of this epitope, occurring in persistent lethal MV strains, were shown to have lost their HLA‐A*0201 binding capacity. Thus, here we report for the first time the direct discovery through μLC‐ESI / MS of a uniquely dominant viral HLA class I ligand, KLWESPQEI, with features eligible for immune selection pressure.

Nanoelectrospray ion trap multiple-stage tandem mass spectrometry was applied to characterize saponins present in HPLC fractions from Quil A, a commercially available bark extract. An analytical strategy was developed based on recognition of carbohydrate sequence ions as well as glycosidic ring-cross ions formed by gamma-hydrogen rearrangements and successive retro-Diels-Alder fragmentations. These ions could be used for the determination of several glycosidic linkages, ring sizes, and positions of acyl groups. The presence of an acyl group on a monosaccharide residue facilitated the determination of the substitution pattern, due to the induction of ring-cross fragmentation. Deuteriomethylation resulted in a more extended set of ring-cross ions, thus allowing determination of additional glycosidic linkages. An analysis typically consumed 200 ng of sample and a total of 1-4 h for measurement and interpretation. The applied method is attractive as a pre-NMR analysis, especially because it resulted rapidly in an overall idea of the structure even when starting from scratch. The multiple-stage tandem approach enabled structural determination of saponins to a more detailed level than achievable with current single-stage tandem mass spectrometry.

A microcapillary column switching high-performance liquid chromatography (HPLC) system was developed for the separation of major histocompatibility complex (MHC) class I associated peptides. Combination of the column switching system with electrospray ionization mass spectrometry (ESIMS) enabled the detection and identification of the peptides at low-femtomole levels. Sample volumes of 30-50 microL were injected and concentrated onto a short, 100-micron-i.d. precolumn. The precolumn was coupled to a 100-micron-i.d. reversed-phase analytical HPLC column via a six-port valve. Peptides were separated on the analytical column using an ESI-compatible mobile phase at a flow rate of 0.5 microL/min. Peptides were eluted directly into the ESI source of either a magnetic sector MS or an ion trap MS. Peptides associated with human leukocyte antigen A*0201 molecules were determined in immunoaffinity-purified extracts from either measles virus infected cells or uninfected cells by microcapillary column switching HPLC-ESIMS. The approach toward detection of virus-specific peptides we used was based on the comparison of ion chromatograms obtained from the LC-MS analysis of extracts from virally infected cells and their uninfected counterparts. In this way, the molecular mass of peptides unique to virus infected cells was obtained. The utility of the system is demonstrated by the identification of a candidate epitope. Microcapillary column switching HPLC was used along with ESI ion trap tandem MS to identify the naturally processed viral peptide KLWESPQEI. This peptide was found to derive from the measles virus nonstructural protein C. The approach described here provides a versatile and sensitive method for the direct identification of viral peptides associated with MHC class I molecules.

Bactericidal antibodies directed against surface loops of class 1 outer membrane proteins play a crucial role in protection against meningitis and sepsis caused by Neisseria meningitidis. So far, all efforts to obtain protective antibodies against these apparently conformational epitopes by using linear peptide analogs have been in vain. In this study, conjugates of head-to-tail cyclic peptides encompassing the predicted top of a protective surface loop were used for immunization. A series of 18 cyclic peptides with a ring size ranging from 7 to 17 residues, conjugated to tetanus toxoid, was investigated. Antipeptide and anti-whole-cell immunoglobulin G (IgG) titers elicited by the conjugates were determined. Conjugates of three peptides, containing 14, 15, and 17 amino acid residues (peptides 7, 12, and 13, respectively), induced an anti-whole-cell titer when Quillaja saponin A was used as the adjuvant. When alum was used as the adjuvant, the conjugate of peptide 12 did not elicit an anti-whole-cell response. From the Quillaja saponin A group, some of the sera obtained with conjugates of peptides 7 and 12 and all sera obtained with the peptide 13 conjugate were bactericidal in vitro. None of the sera evoked with alum as the adjuvant showed bactericidal activity. Nonbactericidal sera contained IgG1 primarily, whereas bactericidal sera showed significant titers of IgG2a and IgG2b. Class 1 protein-derived synthetic cyclic peptides which are capable of eliciting bactericidal antibodies, such as peptide 13 derived from meningococcal strain H44/76, represent potential candidates for a (semi)synthetic vaccine against meningococcal disease.

Intact glucosinolates are separated and identified in standard mixtures and in plant extract of Brussels sprouts by using the liquid chromatography frit to fast-atom bombardment mass spectrometry technique. The separation of the individual glucosinolates is achieved by using a conventional-bore high-performance liquid chromatography column with an aqueous ammonium acetate -acetonitrile gradient. The mandatory flow-rate reduction is achieved by using a pneumatic splitter. The determination limits are estimated to be below 20 pg/g in plant material for various glucosinolates using the sample pretreatment described.

Intact glucosinolates have been separated and identified in standard mixtures using liquid chromatography (LC) and continuowflow frit fast atom bombardment tandem mass spectrometry. The separation of individual glucosinolates is achieved by using a conventional-bore LC column with an aqueous ammonium acetate-acetonitrile gradient. The mandatory flow rate reduction is achieved by using a pneumatic splitter. The daughter ion spectra after collision-induced dissociation of the characteristic [ M -HI -anion of the glucosinolates yields extensive structure information. Both group-and compound-specific fragments and groupcharacteristic neutral losses are observed. Strategies for identification of unknown glucosinolates in a mixture from their negative ion tandem mass spectra are indicated.

Isotope dilution mass spectrometry is one of the best candidates for reference and definitive methods for the quantitative measurement of organic compounds. In this study sources of error were investigated. Where possible they were removed, and commercially available equipment had to be modified. The method was applied to the measurement of serum cholesterol. The precision is optimized and in the order of 0.5%. The mean of the recoveries of three measurements is 99.8%. The accuracy of the mean of three measurements is 0.2% if no interferences are present in the gas chromatographic mass spectrometric measurements.