Bifunctional killing activity encoded by conserved reaper proteins.

Area of Science:

• * Molecular Biology
• * Cell Biology
• * Developmental Biology

Background:

• * Drosophila Reaper proteins are key activators of apoptosis.
• * They function by antagonizing Inhibitor of Apoptosis Proteins (IAPs) via a conserved RHG motif.
• * Understanding the precise mechanisms of Reaper-mediated apoptosis is crucial for cell death research.

Purpose of the Study:

• * To investigate the functional domains of blowfly Reaper and their role in apoptosis.
• * To identify distinct killing activities beyond the known RHG motif.
• * To elucidate the effector pathways involved in Reaper-induced cell death.

Main Methods:

• * Isolation of Reaper from the blowfly *L. cuprina*.
• * Expression of conserved Reaper regions using GFP fusions in *Drosophila* cells.
• * Analysis of apoptosis induction, membrane blebbing, and IAP binding.

Main Results:

• * Blowfly Reaper triggered extensive apoptosis in *Drosophila* cells.
• * A 20-amino acid peptide (R3) conferred a novel killing activity, promoting membrane blebbing independently of translational suppression or DIAP1 levels.
• * A second IAP-binding domain at the C-terminus of Reaper bound DIAP1 but did not induce apoptosis.
• * R3-induced cell death was only modestly suppressed by Dronc silencing and showed no DIAP1 association.

Conclusions:

• * Reaper possesses at least two distinct functional domains mediating cell death.
• * These domains operate through separate effector pathways, challenging single-effector models of Reaper function.
• * Blowfly Reaper represents a conserved bifunctional death-inducing factor.