Identification of actin-binding protein in membrane of polymorphonuclear leukocytes

Abstract

A NEW protein with a high molecular weight and found in rabbit alveolar macrophages¹, causes actin filaments in sucrose solutions to form a solid gel when warmed to room temperature. With transmission electron microscopy, the actin filaments were observed to be bound into branching interconnecting bundles². The new protein was called actin-binding protein (ABP). Similar consistency changes, which are due to gelation of actin associated with other proteins, have been observed in sucrose extracts of Acanthamoeba and glycerol extracts of sea urchin eggs^3,4. ABP was subsequently isolated from extracts of chronic myelogenous leukaemia (CML) leukocytes⁵. The CML leukocyte ABP had identical properties to the analogous protein isolated from the rabbit alveolar macrophage. The CML leukocyte ABP in the presence of actin produced a gel that structurally resembled the hyaline ectoplasm of a pseudopod. Since particle contact with the phagocytic membrane leads to generation of a pseudopod, it seemed reasonable that ABP might be associated with the membrane. Using an antibody directed against CML leukocyte ABP coupled with indirect immunological stains, we were able to localise ABP to the cytoplasmic surface of the membrane of normal polymorphonuclear leukocytes.