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NMR structure and mutagenesis of the FADD (Mort1) death-effector domain
1Pharmaceutical Discovery Division, Abbott Laboratories, Abbott Park, Illinois 60064, USA.
Abstract:
When activated, membrane-bound receptors for Fas and tumour-necrosis factor initiate programmed cell death by recruiting the death domain of the adaptor protein FADD to the membrane. FADD then activates caspase 8 (also known as FLICE or MACH) through an interaction between the death-effector domains of FADD and caspase 8. This ultimately leads to the apoptotic response. Death-effector domains and homologous protein modules known as caspase-recruitment domains have been found in several proteins and are important regulators of caspase (FLICE) activity and of apoptosis. Here we describe the solution structure of a soluble, biologically active mutant of the FADD death-effector domain. The structure consists of six antiparallel, amphipathic alpha-helices and resembles the overall fold of the death domains of Fas and p75. Despite this structural similarity, mutations that inhibit protein-protein interactions involving the Fas death domain have no effect when introduced into the FADD death-effector domain. Instead, a hydrophobic region of the FADD death-effector domain that is not present in the death domains is vital for binding to FLICE and for apoptotic activity.
Insights
Researchers determined the structure of a FADD death-effector domain, revealing a novel hydrophobic region crucial for binding to caspase 8 (FLICE) and initiating programmed cell death (apoptosis). This finding advances understanding of apoptotic signaling pathways.
Area of Science:
- Molecular Biology
- Structural Biology
- Cell Death Research
Background:
- Fas and tumor necrosis factor receptors initiate programmed cell death (apoptosis).
- Adaptor protein FADD recruits caspase 8 (FLICE) via death-effector domains, activating apoptosis.
- Death-effector domains and caspase-recruitment domains regulate caspase activity and apoptosis.
Purpose of the Study:
- To determine the solution structure of a biologically active mutant of the FADD death-effector domain.
- To elucidate the structural basis for FADD-mediated activation of caspase 8 (FLICE).
- To identify key regions within the FADD death-effector domain responsible for apoptotic activity.
Main Methods:
- Solution structure determination of a FADD death-effector domain mutant.
- Analysis of structural similarities and differences with Fas and p75 death domains.
- Mutagenesis studies to assess the role of specific regions in FLICE binding and apoptotic activity.
Main Results:
- The FADD death-effector domain adopts a six antiparallel, amphipathic alpha-helical structure.
- This fold resembles Fas and p75 death domains but differs in functional regions.
- A unique hydrophobic region in the FADD death-effector domain is essential for FLICE binding and apoptotic activity, unlike mutations in Fas death domains.
Conclusions:
- The FADD death-effector domain structure reveals distinct functional determinants for caspase recruitment.
- A novel hydrophobic interaction site is critical for FLICE binding and apoptosis initiation.
- Understanding this mechanism provides insights into regulating programmed cell death pathways.