193 nm Ultraviolet Photodissociation for the Characterization of Singly Charged Proteoforms Generated by MALDI

MALDI imaging allows
for the near-cellular profiling of proteoforms
directly from microbial, plant, and mammalian samples. Despite detecting
hundreds of proteoforms, identification of unknowns with only intact
mass information remains a distinct challenge, even with high mass
resolving power and mass accuracy. To this end, many supplementary
methods have been used to create experimental databases for accurate
mass matching, including bulk or spatially resolved bottom-up and/or
top-down proteomics. Herein, we describe the application of 193 nm
ultraviolet photodissociation (UVPD) for fragmentation of quadrupole
isolated singly charged ubiquitin (m/z 8565) by MALDI-UVPD on a UHMR HF Orbitrap. This platform permitted
the high-resolution accurate mass measurement of not just terminal
fragments but also large internal fragments. The outlined workflow
demonstrates the feasibility of top-down analyses of isolated MALDI
protein ions and the potential toward more comprehensive characterization
of proteoforms in MALDI imaging applications.