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MLKL forms cation channels
Bingqing Xia1, Sui Fang1, Xueqin Chen1
1CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai 201203, China.
Abstract:
The mixed lineage kinase domain-like (MLKL) protein is a key factor in tumor necrosis factor-induced necroptosis. Recent studies on necroptosis execution revealed a commitment role of MLKL in membrane disruption. However, our knowledge of how MLKL functions on membrane remains very limited. Here we demonstrate that MLKL forms cation channels that are permeable preferentially to Mg(2+) rather than Ca(2+) in the presence of Na(+) and K(+). Moreover, the N-terminal domain containing six helices (H1-H6) is sufficient to form channels. Using the substituted cysteine accessibility method, we further determine that helix H1, H2, H3, H5 and H6 are transmembrane segments, while H4 is located in the cytoplasm. Finally, MLKL-induced membrane depolarization and cell death exhibit a positive correlation to its channel activity. The Mg(2+)-preferred permeability and five transmembrane segment topology distinguish MLKL from previously identified Mg(2+)-permeable channels and thus establish MLKL as a novel class of cation channels.
Insights
Mixed lineage kinase domain-like (MLKL) protein forms cation channels, preferentially permeable to magnesium ions (Mg2+), crucial for necroptosis execution. This discovery reveals MLKL as a novel class of ion channels involved in cell death.
Area of Science:
- Cellular biology
- Molecular mechanisms of cell death
- Ion channel biophysics
Background:
- Mixed lineage kinase domain-like (MLKL) protein is essential for necroptosis, a programmed cell death pathway.
- MLKL's precise function in membrane disruption during necroptosis remains incompletely understood.
- Investigating MLKL's membrane interactions is critical for understanding necroptosis execution.
Purpose of the Study:
- To elucidate the membrane channel-forming activity of MLKL.
- To determine the ion permeability and structural topology of MLKL channels.
- To correlate MLKL channel activity with its role in cell death.
Main Methods:
- Biophysical characterization of MLKL-formed channels in membranes.
- Ion permeability assays (Mg2+, Ca2+, Na+, K+).
- Substituted cysteine accessibility method to map transmembrane domains.
- Cellular assays to assess membrane depolarization and cell death.
Main Results:
- MLKL forms cation channels with preferential permeability to Mg2+ over Ca2+.
- The N-terminal domain of MLKL (helices H1-H6) is sufficient for channel formation.
- Helices H1, H2, H3, H5, and H6 are transmembrane segments; H4 is cytoplasmic.
- MLKL-induced membrane depolarization and cell death correlate positively with channel activity.
Conclusions:
- MLKL functions as a novel class of cation channels, distinct from known Mg2+-permeable channels.
- The unique five-transmembrane segment topology and Mg2+-preferred permeability of MLKL channels are key findings.
- MLKL channel activity is directly linked to its role in inducing necroptotic cell death.
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