posted on 2022-01-26, 00:44authored byEmma K. Sisley, Oliver J. Hale, Iain B. Styles, Helen J. Cooper
Label-free spatial
mapping of the noncovalent interactions of proteins
in their tissue environment has the potential to revolutionize life
sciences research by providing opportunities for the interrogation
of disease progression, drug interactions, and structural and molecular
biology more broadly. Here, we demonstrate mass spectrometry imaging
of endogenous intact noncovalent protein–ligand complexes in
rat brain. The spatial distributions of a range of ligand-bound and
metal-bound proteins were mapped in thin tissue sections by use of
nanospray-desorption electrospray ionization. Proteins were identified
directly from the tissue by top-down mass spectrometry. Three GDP-binding
proteins (ADP ribosylation factor ARF3, ARF1, and GTPase Ran) were
detected, identified, and imaged in their ligand-bound form. The nature
of the ligand was confirmed by multiple rounds of tandem mass spectrometry.
In addition, the metal-binding proteins parvalbumin-α and carbonic
anhydrase 2 were detected, identified, and imaged in their native
form, i.e., parvalbumin-α + 2Ca2+ and carbonic anhydrase
+ Zn2+. GTPase Ran was detected with both GDP and Mg2+ bound. Several natively monomeric proteins displaying distinct
spatial distributions were also identified by top-down mass spectrometry.
Protein mass spectrometry imaging was achieved at a spatial resolution
of 200 μm.