Metabolic Labeling-Based Chemoproteomics Establishes Choline Metabolites as Protein Function Modulators

Choline is an essential nutrient for mammalian cells. Our understanding
of the cellular functions of choline and its metabolites, independent
of their roles as choline lipid metabolism intermediates, remains
limited. In addition to fundamental cellular physiology, this knowledge
has implications for cancer biology because elevated choline metabolite
levels are a hallmark of cancer. Here, we establish a mammalian choline
metabolite-interacting proteome by utilizing a photocrosslinkable
choline probe. To design this probe, we performed metabolic labeling
experiments with structurally diverse choline analogues that resulted
in the serendipitous discovery of a choline lipid headgroup remodeling
mechanism involving sequential dealkylation and methylation steps.
We demonstrate that phosphocholine inhibits the binding of one of
the proteins identified, the attractive anticancer target p32, to
its endogenous ligands and to the promising p32-targeting anticancer
agent, Lyp-1. Our results reveal that choline metabolites play vital
roles in cellular physiology by serving as modulators of protein function.