Which secreted molecular species define each EHEC pathway?

Assigning substrates to different EHEC secretion systems requires more than detecting a change in extracellular protein abundance. The discriminating evidence is proteoform-level: secretion-associated signal or propeptide removal, pathway-specific cleavage products, modification states, and intact versus degraded species, alongside controls for lysis and extracellular proteolysis. For this study, the key question is whether system-specific secretion was supported by peptides or termini unique to the released molecular species, rather than by shared peptides that cannot distinguish precursor, processed substrate, and breakdown products. That distinction would determine whether the proteomic signals identify secretion mechanisms or only extracellular accumulation.