Anionic phospholipids are involved in membrane association of FtsY and stimulate its GTPase activity

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Abstract
FtsY, the Escherichia coli homologue of the eukaryotic signal recognition particle (SRP) receptor α‐subunit, is located in both the cytoplasm and inner membrane. It has been proposed that FtsY has a direct targeting function, but the mechanism of its association with the membrane is unclear. FtsY is composed of two hydrophilic domains: a highly charged N‐terminal domain (the A‐domain) and a C‐terminal GTP‐binding domain (the NG‐domain). FtsY does not contain any hydrophobic sequence that might explain its affinity for the inner membrane, and a membrane‐anchoring protein has not been detected. In this study, we provide evidence that FtsY interacts directly with E.coli phospholipids, with a preference for anionic phospholipids. The interaction involves at least two lipid‐binding sites, one of which is present in the NG‐domain. Lipid association induced a conformational change in FtsY and greatly enhanced its GTPase activity. We propose that lipid binding of FtsY is important for the regulation of SRP‐mediated protein targeting.