Homology modelling and ¹H NMR studies of human leukaemia inhibitory factor

Human leukaemia inhibitory factor (LIF) is a glycoprotein with a diverse range of activities on many cell types. A molecular model of LIF has been constructed based mainly on the structure of the related cytokine granulocyte colony-stimulating factor, and refined using simulated annealing and molecular dynamics in water. The model was stable during molecular dynamics refinement and is consistent with known stereochemical data on proteins. It has been assessed by comparison with ¹H NMR data on the ionization behaviour of the six histidine residues in LIF, the imidazolium pK_a values of which range from 3.6 to 7.4. These pK_a values were assigned to individual histidine residues from NMR studies on a series of His → Ala mutants. The environments of the histidine residues in the model account very well for their observed ionization behaviour. Furthermore, the model is consistent with mutagenesis studies which have defined a group of amino acid residues involved in receptor binding.