Fig. 2: Rat and horse MLKL pseudokinase domain structures diverge from mouse MLKL.

a The structure of the human MLKL pseudokinase domain (PDB, 4MWI³⁹) shows a conventional active kinase-like conformation. The K230–E250 salt bridge (equivalent of the K72-E91 PKA interaction) between the β3 ATP-binding lysine and the Glu in the αC helix (shown in dark blue throughout) is shown in the zoomed inset. b The mouse MLKL pseudokinase domain (from PDB 4BTF¹⁸) shows a more open conformation owing to the activation loop adopting an unusual helical conformation (pale blue), which displaces the αC helix (dark blue). An unconventional interaction between the β3 K219 and the activation loop Q343 results (zoomed inset). c The rat MLKL pseudokinase domain adopts an active protein kinase-like conformation, resembling that of the human structure. The β3 K219 forms a conventional salt bridge with the αC helix E239 (zoomed inset), rather than a hydrogen bond with the activation loop Gln observed in the mouse structure. d The horse MLKL pseudokinase domain shows a similar active protein kinase-like conformation, with the K228:E248 salt bridge shown in the zoomed inset. The horse structure exhibits previously unobserved features, including burial of the activation loop in the pseudoactive site and an additional helix in the β3-αC loop (displayed in more detail in Fig. 4).