An inactive protein
that is activated by the removal of one or more polypeptides
. The removal (or cleaving
) is done by proprotein convertases
, whose function is to convert the proprotein to the protein.
The reason that a proprotein is formed, instead of a protein, is that this mechanism ensures that the biologically active molecules are formed in the appropriate cellular compartments. Thus, the proprotein convertases exists in a compartment, and only there can the protein be rendered active by removal of some of its polypeptides.
See also zymogen.