Convertases

Convertases are enzymes that catalyze the transformation of a substrate into a more active or differently functional form. In biology this term is most commonly used for proteolytic enzymes that activate precursor proteins by cleaving them to mature, active forms, and for multi-subunit enzyme complexes that assemble to produce active products from inactive components.

One major group is the proprotein convertases (PCs), a conserved family of subtilisin-like serine proteases that activate a wide range of secreted or membrane-bound proteins by cleaving specific basic residue motifs. They operate mainly in the secretory pathway, particularly the trans-Golgi network and endosomes, and require calcium for activity. Representative members include furin, PC1/3, PC2, PC4, PC5/6, and PC7. Their substrates include prohormones, growth factors, receptors, viral envelope proteins, and precursors to matrix metalloproteinases. Dysregulation of PC activity is linked to developmental disorders, cancer, and infectious disease; inhibitors and modulators are explored for therapeutic use.

Another well-known class is the complement system convertases, enzymes that propagate the innate immune response by activating other complement components. The classical and lectin pathways generate C3 convertases of the form C4b2a, which cleave C3 into C3a and C3b. The alternative pathway produces C3 convertase C3bBb. Addition of C3b to these complexes yields C5 convertases (classical/lectin: C4b2a3b; alternative: C3b2Bb), which cleave C5 into C5a and C5b, leading to inflammation and membrane attack complex formation. These convertases are regulated by factors such as H, I, DAF, and CD59 to protect host tissues.

Additional uses of the term refer to enzyme systems that activate various zymogens or protein complexes in biology, reflecting the general idea of enzymatic activation through proteolysis or assembly.