The pseudokinase MLKL (mixed lineage kinase domain-like) was identified recently as an essential checkpoint in the programmed necrosis or ‘necroptosis’ cell death pathway. In the present study, we report the crystal structure of the human MLKL pseudokinase domain at 1.7 Å (1 Å=0.1 nm) resolution and probe its nucleotide-binding mechanism by performing structure-based mutagenesis. By comparing the structures and nucleotide-binding determinants of human and mouse MLKL orthologues, the present study provides insights into the evolution of nucleotide-binding mechanisms among pseudokinases and their mechanistic divergence from conventional catalytically active protein kinases.