An Optimized Activity-Based Probe for the Study of Caspase-6 Activation

SummaryAlthough significant efforts have been made to understand the mechanisms of caspase activation during apoptosis, many questions remain regarding how and when executioner caspases get activated. We describe the design and synthesis of an activity-based probe that labels caspase-3/-6/-7, allowing direct monitoring of all executioner caspases simultaneously. This probe has enhanced in vivo properties and reduced cross-reactivity compared to our previously reported probe, AB50. Using this probe, we find that caspase-6 undergoes a conformational change and can bind substrates even in the absence of cleavage of the proenzyme. We also demonstrate that caspase-6 activation does not require active caspase-3/-7, suggesting that it may autoactivate or be cleaved by other proteases. Together, our results suggest that caspase-6 activation proceeds through a unique mechanism that may be important for its diverse biological functions.

Graphical AbstractFigure optionsDownload high-quality image (104 K)Download as PowerPoint slideHighlights
► LE22 is an activity-based probe that targets caspase-3, -6, and -7
► Uncleaved caspase-6 has low but detectable levels of catalytic activity
► Complete caspase-6 activation is achieved through multiple maturation steps
► Caspase-6 undergoes a conformational change upon activation and substrate binding