Electron Capture Dissociation Mass Spectrometry of Tyrosine Nitrated Peptides

In vivo protein nitration is associated with many disease conditions that involve oxidative stress and inflammatory response. The modification involves addition of a nitro group at the position ortho to the phenol group of tyrosine to give 3-nitrotyrosine. To understand the mechanisms and consequences of protein nitration, it is necessary to develop methods for identification of nitrotyrosine-containing proteins and localization of the sites of modification.Here, we have investigated the electron capture dissociation (ECD) and collision-induced association (CID) behavior of 3-nitrotyrosine-containing peptides. The presence of nitration did not affect the CID behavior of the peptides. For the doubly-charged peptides, addition of nitration severely inhibited the production of ECD sequence fragments. However, ECD of the triply-charged nitrated peptides resulted in some singly-charged sequence fragments. ECD of the nitrated peptides is characterized by multiple losses of small neutral species including hydroxyl radicals, water and ammonia. The origin of the neutral losses has been investigated by use of activated ion (AI) ECD. Loss of ammonia appears to be the result of non-covalent interactions between the nitro group and protonated lysine side-chains

Crosstalk between Medulloblastoma Cells and Endothelium Triggers a Strong Chemotactic Signal Recruiting T Lymphocytes to the Tumor Microenvironment

Cancer cells can live and grow if they succeed in creating a favorable niche that often includes elements from the immune system. While T lymphocytes play an important role in the host response to tumor growth, the mechanism of their trafficking to the tumor remains poorly understood. We show here that T lymphocytes consistently infiltrate the primary brain cancer, medulloblastoma. We demonstrate, both in vitro and in vivo, that these T lymphocytes are attracted to tumor deposits only after the tumor cells have interacted with tumor vascular endothelium. Macrophage Migration Inhibitory Factor (MIF)” is the key chemokine molecule secreted by tumor cells which induces the tumor vascular endothelial cells to secrete the potent T lymphocyte attractant “Regulated upon Activation, Normal T-cell Expressed, and Secreted (RANTES).” This in turn creates a chemotactic gradient for RANTES-receptor bearing T lymphocytes. Manipulation of this pathway could have important therapeutic implications

Regards de physiciens sur des systemes moleculaires d'interet biologique

IP

On the binding of electrons to nitromethane: Dipole and valence bound anions

Conventional ͑valence͒ and dipole-bound anions of the nitromethane molecule are studied using negative ion photoelectron spectroscopy, Rydberg charge exchange and field detachment techniques. Reaction rates for charge exchange between Cs(ns,nd) and Xe(n f ) Rydberg atoms with CH 3 NO 2 exhibit a pronounced maximum at an effective quantum number of n*Ϸ13Ϯ1 which is characteristic of the formation of dipole-bound anions ͓͑CH 3 NO 2 ͒ϭ3.46 D͔. However, the breadth ͑⌬nϷ5, FWHM͒ of the n-dependence of the reaction rate is also interpreted to be indicative of direct attachment into a valence anion state via a ''doorway'' dipole anion state. Studies of the electric field detachment of CH 3 NO 2 Ϫ formed through the Xe(n f ) reactions at various n values provide further evidence for the formation of both a dipole-bound anion as well as a contribution from the valence bound anion. Analysis of the field ionization data yields a dipole electron affinity of 12Ϯ3 meV. Photodetachment of CH 3 NO 2 Ϫ and CD 3 NO 2 Ϫ formed via a supersonic expansion nozzle ion source produces a photoelectron spectrum with a long vibrational progression indicative of a conventional ͑valence bound͒ anion with a substantial difference in the equilibrium structure of the anion and its corresponding neutral. Assignment of the origin ͑vЈϭ0, vЉϭ0͒ transitions in the photoelectron spectra of CH 3 NO 2 Ϫ and CD 3 NO 2 Ϫ yields adiabatic electron affinities of 0.26Ϯ0.08 and 0.24Ϯ0.08 eV, respectively

On the binding of electrons to nitromethane: Dipole and valence bound anions

Conventional ͑valence͒ and dipole-bound anions of the nitromethane molecule are studied using negative ion photoelectron spectroscopy, Rydberg charge exchange and field detachment techniques. Reaction rates for charge exchange between Cs(ns,nd) and Xe(n f ) Rydberg atoms with CH 3 NO 2 exhibit a pronounced maximum at an effective quantum number of n*Ϸ13Ϯ1 which is characteristic of the formation of dipole-bound anions ͓͑CH 3 NO 2 ͒ϭ3.46 D͔. However, the breadth ͑⌬nϷ5, FWHM͒ of the n-dependence of the reaction rate is also interpreted to be indicative of direct attachment into a valence anion state via a ''doorway'' dipole anion state. Studies of the electric field detachment of CH 3 NO 2 Ϫ formed through the Xe(n f ) reactions at various n values provide further evidence for the formation of both a dipole-bound anion as well as a contribution from the valence bound anion. Analysis of the field ionization data yields a dipole electron affinity of 12Ϯ3 meV. Photodetachment of CH 3 NO 2 Ϫ and CD 3 NO 2 Ϫ formed via a supersonic expansion nozzle ion source produces a photoelectron spectrum with a long vibrational progression indicative of a conventional ͑valence bound͒ anion with a substantial difference in the equilibrium structure of the anion and its corresponding neutral. Assignment of the origin ͑vЈϭ0, vЉϭ0͒ transitions in the photoelectron spectra of CH 3 NO 2 Ϫ and CD 3 NO 2 Ϫ yields adiabatic electron affinities of 0.26Ϯ0.08 and 0.24Ϯ0.08 eV, respectively