Use of Ultraviolet Photodissociation Coupled with Ion Mobility Mass Spectrometry To Determine Structure and Sequence from Drift Time Selected Peptides and Proteins.

We demonstrate the capabilities of a laser-coupled ion mobility mass spectrometer for analysis of peptide sequence and structure showing ultraviolet photodissodation (UVPD) spectra of mass and mobility selected ions. A Synapt G2-S mass spectrometer has been modified to allow photointeraction of ions post the mobility cell. For this work, we have employed a single wavelength laser, which irradiates at 266 nm. We present the unique capabilities of this instrument and demonstrate several key features. Irradiation of luteinizing hormone releasing hormone (LHRH), growth hormone releasing hexapeptide (GHRP-6), and TrpCage (sequence NLYIQWLKDGGPSSGRPPPS) yields extensive b- and y-type fragmentation as well as a- and c-type ions. In addition, we observe side chain losses, induding the indole group from tryptophan, and immonium ions. For negatively charged ions, we show the advantage of using collision-induced dissodation (CLD) post-UVPD: radical ions are produced following irradiation, and these fragment with higher effidency. Further, we have incorporated ion mobility and subsequent drift time gating into the UVPD method allowing the separate analysis of m/z-coinddent spedes, both conformers and multimers. To demonstrate, we selectively dissociate the singly charged dimer or doubly charged monomer of the peptide gramiddin A and conformers of the [M + 5H]S+ form of the peptide melittin. Each mobility selected form has a different "fingerprint" dissodation spectrum, both predominantly containing b and y fragments. Differences in the intensities of various loss channels between the two species were revealed. The smaller conformer of melittin has fewer cleavage sites along the peptide backbone than the larger conformer suggesting considerable structural differences. For gramiddin, a single laser shot UVPD discriminates between primary photodissociation and subsequent fragmentation of fragments. We also show how this modified instrument facilitates activated electron photodissociation. UVPD-IM-MS analysis serves both as a method for peptide sequencing for peptides of similar (or identical) m/z and a method for optical analysis of mobility separated spedes. [ABSTRACT FROM AUTHOR]