The 31-kDa Precursor of Interleukin 1α is Myristoylated on Specific Lysines within the 16-kDa N-Terminal Propiece

The cytokine interleukin 1α (IL-1α) is a critical mediator of the immune and inflammatory responses. A unique determinant of its activity as compared with IL-1β 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 IL-1α precursor is myristoylated on specific internal lysine residues. Immunoprecipitation of [3H]myristic acid-radiolabeled human monocyte lysates with IgG antibodies to the 31-kDa IL-1α precursor recovered a protein with the physicochemical properties of the IL-1α 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 ε-amino groups of lysine. To determine which lysine(s) are acylated, a series of synthetic peptides containing all lysines found in the IL-1α 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-1β propiece was myristoylated with at least 8-fold less efficiency. Acylation of the IL-1α precursor by a previously unrecognized lysyl ε-amino N-myristoyltransferase activity may facilitate its specific membrane targeting.