A constitutively active and uninhibitable caspase-3 zymogen efficiently induces apoptosis

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Caspase-3 zymogen is inactive until cleaved during apoptosis.
• Initiator caspases activate caspase-3 through proteolytic cleavage.
• XIAP (X-linked inhibitor of apoptosis) is an endogenous inhibitor of caspases.

Purpose of the Study:

• To investigate the effect of a V266E mutation on procaspase-3 activity.
• To determine if the pseudo-activated procaspase-3 can be inhibited by XIAP.
• To elucidate the structural basis for the V266E mutation-induced activation.

Main Methods:

• Site-directed mutagenesis to introduce the V266E mutation.
• Enzyme activity assays to measure protease function.
• X-ray crystallography to determine the 1.63 Å structure of the variant.
• Structural modeling to predict the mechanism of activation.

Main Results:

• The V266E mutation pseudo-activates procaspase-3, leading to rapid mammalian cell death at low concentrations.
• Pseudo-activated procaspase-3 is resistant to cleavage and XIAP inhibition.
• The crystal structure reveals the mutation at the dimer interface allows active site formation without cleavage.
• Structural modeling suggests the mutation prevents intersubunit linker binding, facilitating activation.

Conclusions:

• Direct activation of procaspase-3 via a conformational switch is possible.
• The V266E variant exhibits wild-type caspase-3 activity and specificity.
• This pseudo-activation mechanism offers novel therapeutic strategies for inducing apoptosis.