Proximity labelling and cryomill affinity purification compared for Trypanosoma brucei proteins with unconfined, semi-confined and confined localisation

Identification of protein-protein interactions is a major contributor for understanding protein function and elucidating molecular and cellular mechanisms. Two strategies are currently popular for identification of protein interaction partners directly from the cellular environment. Affinity purification (pulldown) isolates the protein of interest with the aid of a matrix that specifically captures the target and potential partners. In BioID, the protein of interest is fused to biotin ligase facilitating proximity biotinylation and biotinylated proteins are isolated under stringent conditions with streptavidin. Whilst clear that these two methods can provide insight, it is also apparent that they can reveal distinct interactomes, but the basis for these differences is less obvious. We compare these methods using four different trypanosome proteins as baits: the cytoplasmic poly(A) binding proteins PABP1 and PABP2, mRNA export receptor MEX67, that shuttles between the nucleus and the cytoplasm with predominant localisation at the nuclear pores, and the nucleoporin NUP158.