THE 31-KDA PRECURSOR OF INTERLEUKIN-1-ALPHA IS MYRISTOYLATED ON SPECIFIC LYSINES WITHIN THE 16-KDA N-TERMINAL PROPIECE

The cytokine interleukin 1alpha (IL-1alpha) is a critical mediator of the immune and inflammatory responses. A unique determinant of its activity as compared with IL-1beta may be its association with the plasma membrane. While the biologic activity of ''membrane IL-1'' has been extensively reported, the mechanism of membrane binding remains unclear. We report that the N terminus of the 31-kDa EL-1alpha precursor is myristoylated on specific internal lysine residues. Immunoprecipitation of [H-3]myristic acid-radiolabeled human monocyte lysates with IgG antibodies to the 31-kDa IL-1alpha precursor recovered a protein with the physicochemical properties of the IL-1alpha N-terminal propiece (16 kDa, pI 4.45). Glycyl N-myristoylation, of this protein is precluded by the absence of a glycine residue at position 2, suggesting that the propiece is myristoylated on epsilon-amino groups of lysine. To determine which lysine(s) are acylated, a series of synthetic peptides containing all lysines found in the IL-1alpha N-terminal propiece were used in an in vitro myristoylation assay containing peptide, myristoyl-CoA, and monocyte lysate as enzyme source. Analysis of the reaction products by reverse-phase HPLC and gas-phase sequencing demonstrated the specific myristoylation of Lys-82 and Lys-83, yielding predominantly monoacylated product. A conserved sequence in the IL-1alpha propiece was myristoylated with at least 8-fold less efficiency. Acylation of the IL-1alpha precursor by a previously unrecognized lysyl epsilon amino N-myristoyltransferase activity may facilitate its specific membrane targeting.