Cassady, Carolyn J. - The University of Alabama

个人简介

Education: Undergraduate Degree A.B., 1979, Pfeiffer College Education: Doctoral Degree Ph.D., 1984, Purdue University Education: Other Postdoctoral Associate, 1988-89, Naval Research Laboratory

研究领域

Mass spectrometry, ion-molecule reactions, dissociation of peptides and proteins ions, FT-ICR and TOF MS/MS analysis The Cassady group uses mass spectrometry to study the gas-phase properties of biomolecules and to develop new techniques for analyzing these compounds. This work involves three state-of-the-art mass spectrometers: a Bruker BioApex 7e Fourier transform ion cyclotron resonance spectrometer (FT-ICR or FTMS), a Bruker Ultraflex I time-of-flight (TOF) spectrometer, and a Bruker HCTultra PTM Discovery System high capacity quadrupole ion trap (QIT). Our FT-ICR research deals with multiply-charged peptide and protein ions produced by electropsray ionization (ESI). Because FT-ICR is a trapping form of mass spectrometry, gas-phase biomolecular ions can be allowed to react with neutral molecules. The ions can also be fragmented, which is useful for obtaining structural information. Most of our recent work has centered on the dissociation of deprotonated peptide ions. These ions are often formed in abundance from peptides with acidic residues, including phosphate or sulfate groups. We study how amino acid composition, acidity, and sequence affects dissociation, with the goal being to develop negative ion MS/MS as a tool for sequencing peptides in proteomics research. Our work often involves peptides of known sequence, which are synthesized in-house with our benchtop peptide synthesizer. Our TOF research involves singly-charged ions produced by matrix-assisted laser desorption ionization (MALDI). The techniques of post-source decay (PSD) and in-source decay (ISD) are used to fragment the ions. The emphasis is on deprotonated peptide ions, as well as metallated ions. The effects of experimental parameters on dissociation are studied. As with our FT-ICR research, we focus on elucidating fragmentation mechanisms and understanding the effects of structural features on dissociation. Molecular dynamics calculations are employed to provide theoretical data that assists in interpreting the experimental results. We are also exploring the use of capped iron oxide nanoparticles as MALDI matrices for organic polymers and biopolymers. Our QIT research involves electron transfer dissociation (ETD) and collision-induced dissociation (CID) of metallated peptide ions produced by ESI. ETD on metallated ions shows great promise as a method for sequencing peptides that are difficult to sequence by more conventional techniques, such as CID on protonated ions. We are exploring how the identity and properties of metal ions affects fragmentation mechanisms. In addition, we are studying the ability of metal salts to increase protonation of peptides by ESI. This “enhanced protonation” affect could make ETD experiments possible on a variety of peptides and other biomolecules that could not previously be studied by ETD.

近期论文

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Effects of Peptide Chain Length on the Gas-Phase Proton Transfer Properties of Doubly Protonated Ions from Bradykinin and its N-Terminal Fragment Peptides", G. A. Pallante and C.J. Cassady, Int J. Mass Spectrom., submitted July 2001. Abstract "Gas-phase Basicities for Ions from Bradykinin and Its des-Arginine Analogues", N.P. Ewing, G.A. Pallante, X. Zhang, and C.J. Cassady, J. Mass Spectrom. 36, 875-881 (2001). Abstract "Dissociation of Multiply-charged Negative Ions for Hirudin (54-65), Fibrinopeptide B, and Insulin A (Oxidized)", N.P. Ewing and C.J. Cassady, J. Am. Soc. Mass Spectrom. 12, 105-116 (2001). Abstract "Gas-Phase Ion Chemistry of Amides, Peptides, and Proteins," C.J. Cassady in The Amide Linkage: Structural Significance in Chemistry, Biochemistry, and Materials Science, A. Greenberg, C. M. Breneman, and J. F. Liebman, eds.; Wiley Interscience, London, pp. 463-494 (2000). "The Freiser Legacy", C. Cassady, J. Am. Soc. Mass Spectrom. 10, 917 (1999). "The Effect of Cysteic Acid Groups on the Gas-Phase Reactivity and Dissociation of [M+4H]4+ Ions from Insulin Chain B," N.P. Ewing and C.J. Cassady, J. Am. Soc. Mass Spectrom. 10, 928-940 (1999). Abstract "Effects of Disulfide Linkages on Gas-phase Reactions of Small Multiply Charged Peptide Ions," J. Wang and C.J. Cassady, Int. J. Mass Spec. 182/183, 233-241 (1999). Abstract "Negative Ion Post-Source Decay Time-of-Flight Mass Spectrometry of Peptides Containing Acidic Amino Acid Residues," J. Jai-nhuknan and C.J. Cassady, Anal. Chem. 70, 5122-5128 (1998). Abstract "Effects of Basic Site Proximity on Deprotonation and Hydrogen/Deuterium Exchange Reactions for Model Dodecapeptide Ions Containing Lysine and Glycine," X. Zhang, N.P. Ewing, and C.J. Cassady, Int. J. Mass Spectrom. Ion Proc. 175, 159-171 (1998). Abstract "Gas-Phase Reactivity and Molecular Modeling Studies on Triply Protonated Dodecapeptide Ions that Contain Four Basic Residues," C.J. Cassady, J. Am. Soc. Mass Spectrom. 9, 716-723 (1998). Abstract "Negative Ion Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Post-Source Decay Calibration Using Fibrinopeptide B," J. Jai-nhuknan and C.J. Cassady, J. Am. Soc. Mass Spectrom. 9, 540-544 (1998). Abstract "Collision-Induced Dissociation and Post-Source Decay of Model Dodecapeptide Ions Containing Lysine and Glycine," X. Zhang, J. Jai-nhuknan, and C.J. Cassady, Int. J. Mass Spectrom. Ion Proc. 171, 135-146 (1997). Abstract "Matrix-assisted Laser Desorption/Ionization of Small Biomolecules Impregnated in Silica Prepared by a Sol-Gel Process," J.B. Laughlin, C.J. Cassady, and J.A. Cox, Rapid Commun. Mass Spectrom. 11, 1505-1508 (1997). Abstract "Reactivity and Gas-Phase Acidity Determinations of Small Peptide Ions Consisting of 11 to 14 Amino Acid Residues," S.R. Carr and C.J. Cassady, J. Mass Spectrom. 32, 959-967 (1997). Abstract "Gas-Phase Basicities of Histidine and Lysine and their Selected Di- and Tripeptides," S.R. Carr and C.J. Cassady, J. Am. Soc. Mass Spectrom. 7, 1203-1210 (1996). Abstract "Determination of the Gas-Phase Basicities of Proline and its Di- and Tripeptides with Glycine: The Enhanced Basicity of Prolylproline," N.P. Ewing, X. Zhang, and C.J. Cassady, J. Mass Spectrom. 31, 1345-1350 (1996). Abstract "Apparent Gas-Phase Acidities of Multiply Protonated Peptide Ions: Ubiquitin, Insulin B and Renin Substrate," X. Zhang and C.J. Cassady, J. Am. Soc. Mass Spectrom. 7, 1211-1218 (1996). Abstract "Anion and Cation Post-Source Decay Time-of-Flight Mass Spectrometry of Small Peptides: Substance P, Angiotensin II, and Renin Substrate," J. Jai-nhuknan and C.J. Cassady, Rapid Commun. Mass Spectrom. 10, 1678-1682 (1996). Abstract "Ab Initio and Experimental Studies on the Protonation of Glucose in the Gas Phase," K.A. Jebber, K. Zhang, C.J. Cassady, and A. Chung-Phillips, J. Am. Chem. Soc. 118, 10515-10524 (1996). Abstract "Elucidation of Isomeric Structures for Ubiquitin [M+12H]12+ Ions Produced by Electrospray Ionization Mass Spectrometry," C.J. Cassady and S.R. Carr, J. Mass Spectrom. 31, 247-254 (1996). Abstract