Validation of the Intermolecular Disulfide Bond in Caspase-2

Simple Summary Caspase-2 belongs to a family of proteins that are involved in cell death pathways. Studies involving caspase-2 have not led to a clear verdict on either the upstream activating signal or the downstream substrates of activated caspase-2. Here, we investigate the unique and highly conserved ability of caspase-2 to form a disulfide-bonded dimer. Disulfide bonds can serve structural roles, but they can also alter the enzymatic activity and localization of proteins within the cytosol. We show that caspase-2 must first dimerize for the disulfide bond to form. This finding suggests that disulfide bond formation is a regulated mechanism of activation. We also investigated various stimuli, some that have been previously published in the context of caspase-2 and some that have not, in caspase-2-deficient cells. Our results show partial protection in caspase-2-deficient cells for some of the stimuli, but a true activating signal, where the loss of caspase-2 is completely protective, has yet to be found.Abstract Caspases are a family of proteins involved in cell death. Although several caspase members have been well characterized, caspase-2 remains enigmatic. Caspase-2 has been implicated in several phenotypes, but there has been no consensus in the field about its upstream activating signals or its downstream protein targets. In addition, the unique ability of caspase-2 to form a disulfide-bonded dimer has not been studied in depth. Herein, we investigate the disulfide bond in the context of inducible dimerization, showing that disulfide bond formation is dimerization dependent. We also explore and review several stimuli published in the caspase-2 field, test ferroptosis-inducing stimuli, and study in vivo infection models. We hypothesize that the disulfide bond will ultimately prove to be essential for the evolved function of caspase-2. Proving this will require the discovery of cell death phenotypes where caspase-2 is definitively essential.