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Papers by Isabel Catalina

International Journal of Mass Spectrometry, 2003

ABSTRACT A set of synthetic phosphorylated peptidomimetic inhibitors of spleen tyrosine kinase (S... more ABSTRACT A set of synthetic phosphorylated peptidomimetic inhibitors of spleen tyrosine kinase (Syk), targeted towards its two tandem Src homology-2 (SH2) domains, was studied by nano-electrospray tandem mass spectrometry in both positive and negative ionisation mode. The design of the peptidomimetic compounds was based on the replacement of the intervening amino acid sequence of a Syk-binding di-phosphopeptide by non-peptide spacers based on either ethylene glycol or amino-propynyl-benzoate. Collision-induced dissociation (CID) spectra of the protonated molecular ions [M+H]+ allowed full characterisation of the peptide hybrids. Preferred cleavage at the amide bond N-terminal to the adjacent polyethylene glycol (PEG) and the propynyl-benzoate (PrB) linkers was observed. In general, it thus appears that preferred sequential amino acid fragmentation takes place from the N-terminus up to the linker molecule followed by subsequent internal fragmentation starting at the C-terminus. Additionally, tandem CID spectra of the doubly de-protonated molecular ions [M–2H]2− of every compound showed the m/z 79/97 phosphate-specific ions plus a remarkably intense ion at m/z 297. The mechanism proposed for the m/z 297-ion occurrence goes through a five-membered ring formation giving an N-terminal pyroGlu structure as derived from MSn spectra.

Journal of Chromatography A, 2000

Journal of Chromatography B-analytical Technologies in The Biomedical and Life Sciences, 2007

Journal of The American Society for Mass Spectrometry, 2005

Journal of Chromatography A, 2002

In the present study the retaining precolumn, which is commonly used in a set-up for large-volume... more In the present study the retaining precolumn, which is commonly used in a set-up for large-volume on-column injections, or when solid-phase extraction (SPE) or liquid chromatography is coupled to gas chromatography (CC), was removed after varying its length from the standard length of 3 m down to zero. A dramatic increase of the evaporation rate of the injected organic solvent was obtained from a typical value of 100 microl/min up to 300 microl/min. The increased evaporation rate allowed (i) injection of a larger volume in the same retention gap, (ii) faster injection/transfer of the organic solvent and (iii) reduction of the transfer temperature. As volatile compounds under partially concurrent solvent evaporation conditions are easily lost once the organic solvent has been removed via a solvent-vapour exit (SVE), the parameters for large-volume injection, i.e. the evaporation rate and injection speed, were optimised using accurate measurements of the real flow-rate of the carrier gas into the GC system. All these options have been evaluated over the last 4 years. In order to demonstrate that omitting the retaining precolumn had no effect on the application range of the on-column interface, analytes as volatile as benzene were injected into GC-MS using 50-200 microl of n-pentane solutions. Contaminants were extracted from river water and wastewater into n-pentane using in-vial liquid-liquid extraction. The detection limits for benzene, toluene, ethylbenzene and m-xylene were approximately 10 ng/l. To obtain optimum results the SVE had to be closed 1 s before the end of evaporation. Several brands of n-pentane were analysed to check for the presence of benzene. Most of them contained interfering compounds and benzene at the low microg/l level and therefore had to be cleaned by means of column chromatography. As another example C8-C17 alkylphenones were extracted from wastewater with n-hexane. Detection limits were 10-40 ng/l.

Rapid Communications in Mass Spectrometry, 2007

The recently introduced electron transfer dissociation (ETD) technique opens new possibilities fo... more The recently introduced electron transfer dissociation (ETD) technique opens new possibilities for the structural characterization of glycoproteins at the glycopeptide level. In this report, we investigate the ETD mass spectra of tryptic N-glycopeptides of the model glycoprotein horseradish peroxidase (HRP). Multiply protonated N-glycopeptides obtained by electrospray ionization were subjected to ETD. Fragment ions obtained by ETD were further analyzed by collision-induced dissociation (CID) (MS3) for their unambiguous structural assignment. The following fragmentation features were revealed: (1) c- and z-type peptide backbone cleavages were observed with retention of the intact glycan moiety revealing peptide sequence, glycan attachment site, and glycan mass; (2) to a lesser extent, glycosidic bond cleavages were registered with retention of the intact peptide sequence; and (3) a range of amino acid side chain losses did occur. Remarkably, the loss of the complete N-glycosylated asparagine side chain was observed. This loss of the glycan-modified side chain helps with the structural characterization of glycopeptides by allowing the facile deduction and verification of the glycan mass and the nature of the amino acid residue at the glycan attachment site. Importantly, informative ETD spectra were obtained in this study by reversed-phase nano-liquid chromatography (LC) coupled online to a radio-frequency (rf) quadrupole ion trap (QIT) mass spectrometer with alternating acquisition of CID and ETD mass spectra from an automatically selected set of precursors (data-dependent mode). Thus, our study brings nano-LC/QIT-MSn with CID and ETD to the fore as a powerful technique for glycoproteomics at the glycopeptide level. Copyright © 2007 John Wiley & Sons, Ltd.

Physical Chemistry Chemical Physics, 2004

Phys. Chem. Chem. Phys., 2004, 6, 2572-2579 DOI:10.1039/B315435A (Paper). Probing factors affecti... more Phys. Chem. Chem. Phys., 2004, 6, 2572-2579 DOI:10.1039/B315435A (Paper). Probing factors affecting the gas phase stabilities of noncovalent complexes formed by peptides bound to the Grb2 SH2 domain protein. M. Isabel ...

Chemistry-a European Journal, 2005

Electrospray ionization mass spectrometry (ESI-MS) is a valuable tool in structural biology for i... more Electrospray ionization mass spectrometry (ESI-MS) is a valuable tool in structural biology for investigating globular proteins and their biomolecular interactions. During the electrospray ionization process, proteins become desolvated and multiply charged, which may influence their structure. Reducing the net charge obtained during the electrospray process may be relevant for studying globular proteins. In this report we demonstrate the effect of a series of inorganic and organic gas-phase bases on the number of charges that proteins and protein complexes attain. Solution additives with very strong gas-phase basicities (GB) were identified among the so-called “proton sponges”. The gas-phase proton affinities (PA) of the compounds that were added to the aqueous protein solutions ranged from 700 to 1050 kJ mol−1. Circular dichroism studies showed that in these solutions the proteins retain their globular structures. The size of the proteins investigated ranged from the 14.3 kDa lysozyme up to the 800 kDa tetradecameric chaperone complex GroEL. Decharging of the proteins in the electrospray process by up to 60 % could be achieved by adding the most basic compounds rather than the more commonly used ammonium acetate additive. This decharging process probably results from proton competition events between the multiply protonated protein ions and the basic additives just prior to the final desolvation. We hypothesize that such globular protein species, which attain relatively few charges during the ionization event, obtain a gas-phase structure that more closely resembles their solution-phase structure. Thus, these basic additives can be useful in the study of the biologically relevant properties of globular proteins by using mass spectrometry.