Figure 9.

Using subtilisin- and MMP-like enzymes in C. reinhardtii and secretory granule-containing cells. The C. reinhardtii genome encodes subtilisin-like proteins resembling the enzymes that cleave proneuropeptides and generate the peptides stored in secretory granules (Table 1). MMP-like proteins resembling those that cleave latent (inactive) growth factor precursors extracellularly are also encoded by the C. reinhardtii genome. Ectosomes released from the cilia of hatching vegetative cells contain active VLE1, the subtilisin-like enzyme that degrades the mother cell wall. Latent growth factor activation in vertebrates involves extracellular activation of MMPs, along with the interaction of proteases and growth factors with the extracellular matrix and plasma membrane. The presence of secretory granules allows control of zymogen activation by declining luminal pH and storage of active peptides for release in response to secretagogues.