An improved TurboID pipeline in C. elegans by biochemical depletion of endogenously biotinylated carboxylases
Proximity-dependent protein labeling provides a powerful in vivo strategy to characterize the interactomes of specific proteins. We previously optimized a proximity labeling protocol for C. elegans using the highly active biotin ligase TurboID. A significant constraint on the sensitivity of TurboID is the presence of abundant, endogenously biotinylated proteins that take up bandwidth in the mass spectrometer, notably carboxylases that use biotin as a co-factor. In C. elegans, these comprise POD-2/acetyl-CoA carboxylase alpha, PCCA-1/propionyl-CoA carboxylase alpha, PYC-1/pyruvate carboxylase and MCCC-1/methylcrotonyl-CoA carboxylase alpha. We developed ways to remove these carboxylases prior to streptavidin purification and mass spectrometry, by engineering their corresponding genes to add a C-terminal His10 tag. This allows us to deplete them from C. elegans lysates using immobilized metal affinity chromatography (IMAC). To demonstrate the methods efficacy, we use it to expand the interactome map of the presynaptic active zone protein ELKS-1. We identify many known active zone proteins, as well as previously uncharacterized potentially synaptic proteins. Our approach provides a quick and inexpensive solution to a common contaminant problem in biotin- dependent proximity labeling. The approach may be applicable to other model organisms and will enable deeper and more complete analysis of interactors for proteins of interest.