Preparation of Myristoylated Arf1 and Arf6 Proteins

ADP-ribosylation factor (Arf) proteins were first identified as cofactors for cholera toxin-catalyzed ADP-ribosylation of the heterotrimeric G-protein Gs. Subsequent cloning led to the discovery that Arfs were part of a group of GTP-binding proteins that is a subfamily of the ras superfamily. The Arf family is comprised of the Arf proteins and related Arf-like (Arl) proteins. Activity as cofactors for cholera toxin distinguishes the Arf proteins from the Arls. The Arf proteins can be further subdivided into class I (comprised of Arf 1 and Arf3 in humans), class II (comprised of Arf4 and Arf5), and class III (comprised of Arf6). Arfs have been found in all eukaryotes studied. Multiple Arf proteins occur within single organisms and within single cells, and Arf orthologs are highly conserved between species. The most extensively studied mammalian Arfs are Arf 1 and Arf6, which have been found to function as regulators of membrane traffic and the actin cytoskeleton (1 –9 ). In biochemical studies, Arfs have also been found to activate phospholipase D (PLD) and phosphatidylinositol 4-phosphate 5-kinase, and to bind to several putative effectors such as arfaptin, arfophilin, and the GGAs (10 –20 ). Unlike other ras family members which are prenylated at the C-terminus, Arfs are myristoylated on an N-terminal glycine in a cotranslational event catalyzed by N-myristoyl transferase (NMT) (21 –24 ). This lipid modification is crucial for activity.