There has been growing interest in employing top-down approaches to directly interrogate native-like protein structures, primarily using MS/MS methods to disassemble the complexes, sequence the proteins, and draw conclusions about protein conformation based on fragmentation behavior. Ultraviolet photodissociation (UVPD) in particular has provided unsurpassed levels of sequence coverage for intact proteins and has recently exhibited similar levels of performance for native-like proteins and protein complexes. The abundances of sequence ions created by UVPD mirror the B-factors of native proteins, and products retaining non-covalently bound ligands are observed. Here we describe the use of photodissociation in conjunction with charge-reduction reactions to compare protein structures folded in the gas phase to more native-like structures from native (non-denaturing) electrospray.
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