The influence of the methionine residue on the dissociation mechanisms of photoionized methionine-enkephalin probed by VUV action spectroscopy

Abstract

VUV action spectroscopy has recently gained interest for the study of peptides and proteins. However, numerous aspects of the fundamental processes involved in the photodissociation are yet to be understood. It can, for example, be expected that sulfur-containing amino-acid residues have a significant impact on the dissociation processes following photoionization because of their potential involvement in the transport of electron holes in proteins. In order to investigate the influence of the sulfur-containing methionine residue on the VUV photodissociation of a small peptide a VUV action spectroscopy study of gas-phase protonated methionine-enkephalin and leucine-enkephalin in the photon energy range of 6–35 eV was performed. The results show that upon non-ionizing photoexcitation, the fragmentation patterns of the two peptides are nearly identical, whereas significant differences were observed upon photoionization. The differences between the fragment yields and the identified specific dissociation channels for methionine-enkephalin could be explained by the high electron hole affinity of sulfur, which efficiently directs the radical to the methionine side chain. Additionally, for both peptides the presence of the intact photoionized precursor ions was confirmed by their isotopic patterns and the stability of these species could be evaluated. Graphic abstract

Mapping the electronic transitions of protonation sites in peptides using soft X-ray action spectroscopy

“…NEXAMS, or TIY NEXAFS, has been extensively used and compared with X-ray absorption calculations. 17,18,[30][31][32][33][34][35]…”

Photodissociation of leucine-enkephalin protonated peptide: an experimental and theoretical perspective

“…LeuEnk has become a mass spectrometry standard, 48 and there is a plethora of papers having studied its fragmentation induced by different activation techniques, including collisional induced dissociation (CID) 48 and UV/VUVinduced fragmentation. 33,34,[49][50][51] LeuEnk is a large enough molecule to be a good model for biologically important peptides and at the same time small enough (MH + = 556 Da) to be studied from a theoretical point of view.…”