Okay, it's back to the metaphor! Whether you're Dr. Hall
trying to nuke the Wildfire laboratory to prevent the Andromeda Strain from
eating the world, or Ripley trying to blow up yet another space ship to stop
the Aliens, or Captain Kirk sacrificing the Enterprise to waste a few
Klingons….you're going to need a bomb. That is, you need an executioner.
If you're a worm, that means you need a ced-3 gene product. If you're Ripley
or Captain Kirk, you need the mammalian equivalent, which is a caspase.
Caspases are a family of proteases, and they come in a lot
of different flavors. But they all have several things in common:
- They are
synthesized in their inactive form as monomers with prodomains of varying
- They require cleavage to be activated, and
- When cleaved they
form active heterotetramers. In the animation below, notice how cleavage of the
prodomain of the caspase brings about exposure and completion of the active
site, and how homodimerization creates a monster.
Animation. How cleavage activates caspases to screw up your day.