Protein post-translational modification signature true beta12orEarlier A protein post-translational modification signature corresponds to sites that undergo modification of the primary structure, typically to activate or de-activate a function. For example, methylation, sumoylation, glycosylation etc. The modification might be permanent or reversible. 1.4 A protein post-translational modification signature (sequence classifier) from the InterPro database. Sequence motif (protein)