Effects of l-Histidine and Its Structural Analogues on Human N-Myristoyltransferase Activity and Importance of EEVEH Amino Acid Sequence for Enzyme Activity

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Abstract
Myristoyl-CoA:protein N-myristoyltransferase (NMT) is an essential eukaryotic enzyme that catalyzes the cotranslational transfer of myristate to the NH2-terminal glycine residue of a number of important proteins of diverse function. Human NMT (hNMT) activity was found to be activated by l-histidine in a concentration-dependent manner. In contrast, two structural analogues of l-histidine, l-histidinol and histamine, inhibited hNMT activity in a noncompetitive manner with half-maximal inhibitions of 18 and 1.5 mM, respectively. The inhibition of hNMT activity by l-histidinol was reversed by a 2-fold molar excess of l-histidine, suggesting that l-histidine and l-histidinol were competing for a common site on NMT. Kinetic data indicated that whereas l-histidine enhanced the Vmax, both l-histidinol and histamine decreased the Vmax; none of these compounds altered the Km. Our studies suggest that l-histidine and its analogues may be interacting with His-293, involved in myristoyl-CoA transfer, rather than His-218, and implicated in the transfer of myristoyl-CoA to the peptide substrates. Site-directed mutagenesis of His-293, Val-291, and Glu-290 resulted in proteins with no measurable NMT activity. The most conserved region in the catalytic domain EEVEH (289−293) is critical for the myristoyl-CoA transfer in the NMT-catalyzed reactions. This region will be useful for the design of regulators of NMT function.

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