Analysis of a chlorosulfolipid from Ochromonas danica by matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight mass spectrometry.

Matrix-assisted laser desorption/ionization (MALDI) time-of-flight (ToF) mass spectrometry (MS) is an established tool for analyzing high mass molecules, such as proteins, whereas it attracts far less interest in the field of lipid analysis. In the study reported here a new chlorosulfolipid (CSL), 3,8,12,15-tetrachloroeicosane-1,17,18-triyl tris(hydrogen sulfate), was identified from the alga Ochromonas danica and de novo characterized by matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight (MALDI-QIT-ToF) MS in negative ion mode. This method provides an effective alternative for the analysis of compounds directly derived from organic cell extracts. For MALDI analyses several frequently used solid MALDI matrices as well as some ionic liquid matrices (ILMs) were tested to enhance the analyte response to UV-laser and its ionization. The molecular weight of the observed compound could be determined as Li-, Na- and K-adducts [M+Me-2H]-. The characteristic isotopic patterns of the measured ions and the well-allocated molecular fragments by MS1, MS2 and MS3 indicate the fourfold chlorination and threefold sulfation of the investigated compound. The MS fragmentation alongside of the chlorine-bearing C-atoms is accompanied by the generation of a double bond at the opposite fragment in MS1. This obtained fragmentation pattern provides an insight into the allocation of the chlorine-bearing C-atoms along the carbon chain.

Analysis of N-linked glycans of porcine zona pellucida glycoprotein ZPA by MALDI-TOF MS: a contribution to understanding zona pellucida structure.

The mammalian oocyte is encased by a transparent extracellular matrix, the zona pellucida (ZP), which consists of three glycoproteins, ZPA, ZPB, and ZPC. The glycan structures of the porcine ZP and the complete N-glycosylation pattern of the ZPB/ZPC oligomer has been recently described. Here we report the N-glycan pattern and N-glycosylation sites of the porcine ZP glycoprotein ZPA of an immature oocyte population as determined by a mass spectrometric approach. In-gel deglycosylation of the electrophoretically separated ZPA protein and comparison of the pattern obtained from the native, the desialylated and the endo-beta-galactosidase-treated glycoprotein allowed the assignment of the glycan structures by MALDI-TOF MS by considering the reported oligosaccharide structures. The major N-glycans are neutral biantennary complex structures containing one or two terminal galactose residues. Complex N-glycans carrying N-acetyllactosamine repeats are minor components and are mostly sialylated. A significant signal corresponding to a high-mannose type chain appeared in the three glycan maps. MS/MS analysis confirmed its identity as a pentamannosyl N-glycan. By the combination of tryptic digestion of the endo-beta-galactosidase-treated ZP glycoprotein mixture and in-gel digestion of ZPA with lectin affinity chromatography and reverse-phase HPLC, five of six N-glycosylation sites at Asn(84/93), Asn268, Asn316, Asn323, and Asn530 were identified by MS. Only one site was found to be glycosylated in the N-terminal tryptic glycopeptide with Asn(84/93.) N-glycosidase F treatment of the isolated glycopeptides and MS analysis resulted in the identification of the corresponding deglycosylated peptides.

Primary structure details of haptoglobin alpha chain proteins from human plasma samples are resolved by matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight multiple-stage tandem mass spectrometry sequencing.

MALDI QIT ToF MS(n) analyses lead to the rapid identification of protein structural details, as readily interpretable spectra after peptide fragmentations were obtained showing ion signals with high abundance even with sample amounts in the low femtomole range. In our studies we show that the Hp alpha 1F form that contained a C-terminal arginine residue was found to be the only contributing component to spot 149. By contrast, spots 77 and 79 were found to consist of two haptoglobin forms each. Spot 77 consists of Hp alpha 1S and deamidated Hp alpha 1F, whereas spot 79 consists of Hp alpha 1F and of Hp alpha 1S that contains a C- terminal arginine residue. The use of ion traps, enabling the acquisition of MSn spectra serves as a powerful peptide sequencing method for the analysis of both, genetic differences and post-translational modification events as the main reason for the observed spot pattern in the 2-D gels of haptoglobin proteins.

Matrix-assisted laser desorption/ionization- quadrupole ion trap-time of flight mass spectrometry sequencing resolves structures of unidentified peptides obtained by in-gel tryptic digestion of haptoglobin derivatives from human plasma proteomes.

Two-dimensional gel electrophoresis-separated and excised haptoglobin alpha2-chain protein spots were subjected to in-gel digestion with trypsin. Previously unassigned peptide ion signals observed in mass spectrometric fingerprinting experiments were sequenced using the matrix-assisted laser desorption/ionization-quadrupole ion trap-time of flight (MALDI-QIT-TOF) mass spectrometer and showed that the haptoglobin alpha-chain derivative under study was cleaved by trypsin unspecifically. Abundant cleavages occurred C-terminal to histidine residues at H23, H28, and H87. In addition, mild acidic hydrolysis leading to cleavage after aspartic acid residues at D13 was observed. The uninterpreted tandem mass spectrometry (MS/MS) spectrum of the peptide with ion signal at 2620.19 was submitted to database search and yielded the identification of the corresponding peptide sequence comprising amino acids (aa) aa65-87 from the haptoglobin alpha-chain protein. Also, the presence of a mixture of two tryptic peptides (mass to charge ratio m/z 1708.8; aa40-54, and aa99-113, respectively), that is caused by a tiny sequence variation between the two repeats in the haptoglobin alpha2-chain protein was resolved by MS/MS fragmentation using the MALDI-QIT-TOF mass spectrometer instrument. Advantageous features such as (i) easy parent ion creation, (ii) minimal sample consumption, and (iii) real collision induced dissociation conditions, were combined successfully to determine the amino acid sequences of the previously unassigned peptides. Hence, the novel mass spectrometric sequencing method applied here has proven effective for identification of distinct molecular protein structures.