Ionization state and molecular docking studies for the macrophage migration inhibitory factor: the role of lysine 32 in the catalytic mechanism

The macrophage migration inhibitory factor (MIF) is a cytokine that is stru cturally similar to certain isomerases and for which multiple immune and ca talytic roles have been proposed. Different catalytic activities have been reported for MIF, yet the exact mechanism by which MIF acts is not complete ly known. As a tautomerase, the enzyme uses a general acid-base mechanism o f proton transfer in which the aminoterminal proline has been shown to func tion as the catalytic base. We report the results of molecular docking simu lations of macrophage migration inhibitory factor with three substrates, D- dopachrome, L-dopachrome methyl ester and p-(hydroxyphenyl)pyruvate. Electr ostatic pK(a) predictions were also performed for the free and complexed fo rms of the enzyme. The predicted binding mode of p-(hydroxyphenyl)pyruvate is in agreement with the recently published X-ray structure. A model for th e binding mode of D-dopachrome and L-dopachrome methyl ester to MIF is prop osed which offers insights into the catalytic mechanism of D-dopachrome tau tomerase activity of MIF. The proposed catalytic mechanism is further suppo rted by the pK(a) predictions, which suggest that residue Lys32 acts as the general acid for the enzymatic catalysis of D-dopachrome., Copyright (C) 2 000 John Wiley & Sons.