Similar Membrane Affinity of Mono- and Di-S-acylated Ras Membrane Anchors: A New Twist in the Role of Protein Lipidation

Membrane targeting through posttranslational lipid modification is essential for the function of many signaling proteins, such as the GTPase Ras.1 Lipid modification in Ras involves an irreversible isoprenylation of a C-terminal Cys supplemented by a polybasic domain (K-ras) or a reversible modification of adjacent Cys residues by one (N-ras) or two (H-ras) palmitoyls.2 Kinetic studies have shown that the intervesicle transfer of doubly lipid-modified peptides is faster than their singly lipidated counterparts.3 However, the notion that multiple lipidation invariably confers tighter membrane binding has not been systematically scrutinized. As a result, whether the triply lipidated membrane anchor of H-ras (residues Gly180-Cys181-Met182-Ser183-Cys184-Lys185-Cys186-OCH3) has a higher membrane affinity than its doubly lipidated counterpart, or whether the affinity contribution of Cys181-palmitate, Cys184-palmitate, and Cys186-farnesyl is additive, was not known. Furthermore, th