CALCIUM-DEPENDENT BINDING OF PHOSPHORYLATED HUMAN PRE-INTERLEUKIN-1-ALPHA TO PHOSPHOLIPIDS

The effect of phosphorylation of pre interleukin la (IL la) on its association with various phospholipids was investigated. We prepared genetically engineered truncated human pre IL la (residues 64 to 271) and phosphorylated this pre IL la in vitro by using the catalytic subunit of cAMP-dependent protein kinase. Phosphorylated truncated pre IL la selectively binds to acidic phospholipids including phosphatidic acid, phosphatidylserine, and phosphatidylinositol, but not to other phospholipids (phosphatidylcholine and phos-phatidylethanolamine). This binding required divalent cations: Ca2+ or Mn2+, but not Mg2+. In order to obtain half-maximal binding of pre IL la to phosphatidic acid or phosphatidylserine, Ca2+ between 5 and 100 m^M was required. Unphosphorylated pre IL la did not bind to phosphatidylserine, indicating that phosphorylation is required for this binding. Phosphorylated pre IL 1 α did not bind to intact peripheral blood mononuclear cells irrespective of lipopolysaccharide stimulation, but did bind to membrane vesicles prepared from these cells in the presence of calcium. Furthermore, phosphorylated pre IL la bound only to inside-out ghosts, but not right-side-out ghosts, prepared from human red blood cells. Taken together, these data suggest that phosphorylated pre IL la binds to the inner surface of plasma membrane in a Ca2+ and phospholipid-dependent manner. © 1990 COPYRIGHT, 1990 BY THE JOURNAL OF BIOCHEMISTRY.