Mapping the cytosolic proteins of HEK293T cells

N-terminal proteoforms stem from the same gene but differ at their N-terminus, and most of these are found to be truncated, though some are N-terminally extended caused by ribosomes starting translation from codons in the annotated 5’UTR, and/or carry modified N-termini different from those of the canonical protein. Biological functions of N-terminal proteoforms are emerging, however, it remains unknown to what extend N-terminal proteoforms further expand the functional complexity. To address this in a more global manner, we mapped the interactomes of several pairs of N-terminal proteoforms and their canonical counterparts. For this, we first generated an in-depth catalogue of N-terminal proteoforms in the cytosol of HEK293T cells. In order to aid the selection of pairs of N-terminal proteoforms we generated a cytosolic map to verify their cytosolic interactions. This localization is crucial as Virotrap will be used for interactome analysis and this method works best for cytosolic proteins.