Effects of Charge State and Cationizing Agent on the Electron Capture Dissociation of a Peptide

Electron capture dissociation (ECD) is a promising method for de novo sequencing proteins and peptides and for locating the positions of labile posttranslational modifications and binding sites of noncovalently bound species. We report the ECD of a synthetic peptide containing 10 alanine residues and 6 lysine residues uniformly distributed across the sequence. ECD of the (M + 2H) 2+ produces a limited range of c (c 7 -c 15 ) and z (z 9 -z 15 ) fragment ions, but ECD of higher charge states produces a wider range of c (c 2 -c 15 ) and z (z 2 -z 6 , z 9 -z 15 ) ions. Although mass spectrometry (MS) and tandem mass spectrometry (MS/MS) have been used to characterize peptides for more than three decades, 1,2 the developments of electrospray ionization (ESI) 3 and matrix-assisted laser desorption/ionization 4 have dramatically expanded the size and type of molecules amenable to characterization by MS/MS. For example, ESI has been used to form intact gas-phase ions from virus particles (4.0 × 10 7 Da) 5 and DNA molecules as large as 1.2 × 10 8 Da. 6 ESI-MS and ESI-MS/MS experiments can be performed using as little as 10 -18 mol of sample. 7 For these measurements, Fourier transform (FT) MS has the advantages of ultrahigh resolution, multichannel detection, and MS n capabilities. 8,9 Dissociation methods in FTMS, including collisionally activated dissociation (CAD), 10 surface-induced dissociation, 11,12 infrared multiphoton dissociation, 13 and blackbody infrared radiative dissociation, 14,15 have been used to obtain sequence information and locations of posttranslational modifications (PTMs) in biomolecules. With these activation methods, the most labile bonds within an ion are typically cleaved. This often produces incomplete sequence coverage, the loss of PTMs, and a lack of backbone cleavages within regions enclosed by disulfide bridges. The recently developed method of electron capture dissociation (ECD), [16][17][18][19][20][21][22][23][24][25

Efficiency of Collisionally-activated dissociation and 193-nm photodissociation of peptide ions in fourier transform mass spectrometry

AbstractFor tandem mass spectrometry, the Fourier transform instrument exhibits advantages for the use of collisionally-activated dissociation (CAD). The CAD energy deposited in larger ions can be greatly increased by extending the collision time to as much as 120 s, and the efficiency of trapping and measuring CAD product ions in many times greater than the found for triple-quadrupole or magnetic sector instruments, although the increased pressure from the collision gas is an offsetting disadvantage. A novel system that uses the same laser for photodesorption of ions and their subsequent photodissociation can produce complete dissociation of larger oligopeptide ions and unusually abundant fragment ions. In comparison to CAD, much more internal energy can be deposited in the primary ions using 193-nm photons, sufficient to dissociate peptide ions of m/z > 2000. Mass spectra closely resembling ion photodissociation spectra can also be obtained by neutral photodissociation (193-nm laser irradiation of the sample) followed by ion photodesorption

Liquid Chromatography Electron Capture Dissociation Tandem Mass Spectrometry (LC-ECD-MS/MS) versus Liquid Chromatography Collision-induced Dissociation Tandem Mass Spectrometry (LC-CID-MS/MS) for the Identification of Proteins

Electron capture dissociation (ECD) offers many advantages over the more traditional fragmentation techniques for the analysis of peptides and proteins, although the question remains: How suitable is ECD for incorporation within proteomic strategies for the identification of proteins? Here, we compare LC-ECD-MS/MS and LC-CID-MS/MS as techniques for the identification of proteins.Experiments were performed on a hybrid linear ion trap–Fourier transform ion cyclotron resonance mass spectrometer. Replicate analyses of a six-protein (bovine serum albumin, apo-transferrin,lysozyme, cytochrome c, alcohol dehydrogenase, and β-galactosidase) tryptic digest were performed and the results analyzed on the basis of overall protein sequence coverage and sequence tag lengths within individual peptides. The results show that although protein coverage was lower for LC-ECDMS/MS than for LC-CID-MS/MS, LC-ECD-MS/MS resulted in longer peptide sequence tags,providing greater confidence in protein assignment

Optimizing the two-step floating catchment area method for measuring spatial accessibility to medical clinics in Montreal

<p>Abstract</p> <p>Background</p> <p>Reducing spatial access disparities to healthcare services is a growing priority for healthcare planners especially among developed countries with aging populations. There is thus a pressing need to determine which populations do not enjoy access to healthcare, yet efforts to quantify such disparities in spatial accessibility have been hampered by a lack of satisfactory measurements and methods. This study compares an optimised and the conventional version of the two-step floating catchment area (2SFCA) method to assess spatial accessibility to medical clinics in Montreal.</p> <p>Methods</p> <p>We first computed catchments around existing medical clinics of Montreal Island based on the shortest network distance. Population nested in dissemination areas were used to determine potential users of a given medical clinic. To optimize the method, medical clinics (supply) were weighted by the number of physicians working in each clinic, while the previous year's medical clinic users were computed by ten years age group was used as weighting coefficient for potential users of each medical clinic (demand).</p> <p>Results</p> <p>The spatial accessibility score (SA) increased considerably with the optimisation method. Within a distance of 1 Km, for instance, the maximum clinic accessible for 1,000 persons is 2.4 when the conventional method is used, compared with 27.7 for the optimized method. The t-test indicates a significant difference between the conventional and the optimized 2SFCA methods. Also, results of the differences between the two methods reveal a clustering of residuals when distance increases. In other words, a low threshold would be associated with a lack of precision.</p> <p>Conclusion</p> <p>Results of this study suggest that a greater effort must be made ameliorate spatial accessibility to medical clinics in Montreal. To ensure that health resources are allocated in the interest of the population, health planners and the government should consider a strategy in the sitting of future clinics which would provide spatial access to the greatest number of people.</p