38 research outputs found
Novel CĪ²āCĪ³ Bond Cleavages of Tryptophan-Containing Peptide Radical Cations
In this study, we observed unprecedented cleavages of the CĪ²āCĪ³ bonds of tryptophan residue side chains in a series of hydrogen-deficient tryptophan-containing peptide radical cations (Mā¢+) during low-energy collision-induced dissociation (CID). We used CID experiments and theoretical density functional theory (DFT) calculations to study the mechanism of this bond cleavage, which forms [M ā 116]+ ions. The formation of an Ī±-carbon radical intermediate at the tryptophan residue for the subsequent CĪ²āCĪ³ bond cleavage is analogous to that occurring at leucine residues, producing the same product ions; this hypothesis was supported by the identical product ion spectra of [LGGGH ā 43]+ and [WGGGH ā 116]+, obtained from the CID of [LGGGH]ā¢+ and [WGGGH]ā¢+, respectively. Elimination of the neutral 116-Da radical requires inevitable dehydrogenation of the indole nitrogen atom, leaving the radical centered formally on the indole nitrogen atom ([Ind]ā¢-2), in agreement with the CID data for [WGGGH]ā¢+ and [W1-CH3GGGH]ā¢+; replacing the tryptophan residue with a 1-methyltryptophan residue results in a change of the base peak from that arising from a neutral radical loss (116Ā Da) to that arising from a molecule loss (131Ā Da), both originating from CĪ²āCĪ³ bond cleavage. Hydrogen atom transfer or proton transfer to the Ī³-carbon atom of the tryptophan residue weakens the CĪ²āCĪ³ bond and, therefore, decreases the dissociation energy barrier dramatically
Nidogen 1-enriched extracellular vesicles facilitate extrahepatic metastasis of liver cancer by activating pulmonary fibroblasts to secrete tumor necrosis factor receptor 1
202009 bcrcVersion of RecordPublishe