Sensitive β-substituted aliphatic Ile/Val-Xxx and aromatic Phe/Tyr/His-Xxx residues to form [a]+ ions in high energy CID of peptides

Abstract

Residue-specific cleavages resulting in the formation of [a]+ ions of peptides have been examined using 20 keV high-energy (high-E) collision-induced dissociation (CID) with a tandem time-of-flight (TOF/TOF) instrument. High-E CID resulted in relatively sensitive cleavage at the Cα-C bond of β-substituted aliphatic Val/Ile-Xxx and aromatic Phe/Tyr/His-Xxx residues when an Arg residue was located on the N-terminal side. The sensitive aromatic Phe/Tyr/His residues and insensitive Gly residue in high-E CID are similar to other methods, such as ultraviolet photodissociation (UVPD) of [M+H]+, low-E CID of [M].+ and MALDI-ISD with a hydrogen-abstracting matrix. The properties of the Val/Ile residues are not necessarily common to the same methods. The high-sensitivity of Val/Ile and Phe/Tyr/His residues to high-E CID may be due to high-energy single collision between target gas and the bulky sidechains of these residues. It is suggested that from high-E CID and MALDI-ISD experiments the formation of [a]+ ions is essentially connected with the loss of atomic hydrogen from protonated peptides [M+H]+, and that high-E CID results in the loss of hydrogen from the backbone amide nitrogen rather than the site of the β-carbon of sidechains.