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Description

Mixed lineage kinase domain-like protein (UniProt: Q9D2Y4, also known as MLKL) is encoded by the Mlkl gene (Gene ID: 74568) in murine species. MLKL is a pseudokinase that is a terminal protein in the pro-inflammatory necroptotic cell death program. It plays a critical role in TNFa-induced necroptosis. It is highly expressed in thymus, colon, intestine, liver, spleen, and lung. Its expression is much lower in skeletal muscle, heart and kidney, and it is not detected in the brain. Although it contains a protein kinase domain (aa 192-456), it lacks several residues that are essential for protein kinase activity. It is activated following phosphorylation by RIPK3, which leads to its homotrimerization and localization to the plasma membrane where it binds to highly phosphorylated inositol (InsP6) and disrupts membrane integrity to cause necrotic cell death. Phosphorylation of MLKL at serine 345 is shown to be essential for necroptosis in murine cells. Its interaction with RIPK3 is species specific and mouse MLKL does not interact with human RIPK3. In contrast to human protein, mouse MLKL is not inhibited by necrosulfonamide, because at position 85 it contains a tryptophan residue instead of a cysteine. Under basal conditions, MLKL is shown to reside in small puncta that are distributed evenly throughout the cytoplasm, but it is detected in plasma membrane shortly after its phosphorylation. It contains two coiled coil regions (aa 61-81 and 138-229) and the second coiled coil region is responsible for its oligomerization. Two isoforms of MLKL have been described that are produced by alternative splicing. (Ref.: Samson, AL., et al. (2021). Cell Death Differ. 28(7), 2126-2144, Wang, H., et al (2014). Mol. Cell 54(1), 133-146).