Tracking Inhibition of Human Small C‑Terminal Domain Phosphatase 1 Using 193 nm Ultraviolet Photodissociation Mass Spectrometry

Working in tandem
with kinases via a dynamic interplay of phosphorylation
and dephosphorylation of proteins, phosphatases regulate many cellular
processes and thus represent compelling therapeutic targets. Here
we leverage ultraviolet photodissociation to shed light on the binding
characteristics of two covalent phosphatase inhibitors, T65 and rabeprazole,
and their respective interactions with the human small C-terminal
domain phosphatase 1 (SCP1) and its single-point mutant C181A, in
which a nonreactive alanine replaces one key reactive cysteine. Top-down
MS/MS analysis is used to localize the binding of T65 and rabeprazole
on the two proteins and estimate the relative reactivities of each
cysteine residue.