FtsY

FtsY is the bacterial signal recognition particle (SRP) receptor. It functions with the SRP protein Ffh and the SRP RNA to target ribosome-nascent chain complexes to the inner membrane for cotranslational protein targeting to the Sec translocon.

The protein has a two-domain architecture. An N-terminal A-domain is acidic and flexible, mediating membrane association, while a C-terminal NG-domain contains the GTPase fold that binds GTP and interacts with Ffh. This arrangement allows FtsY to shuttle between cytosolic and membrane-associated states, with membrane docking largely mediated by the A-domain and functional engagement with the SRP complex through the NG-domain.

Mechanistically, SRP recognizes a signal sequence on a translating ribosome and pauses translation. The SRP–ribosome complex is delivered to the inner membrane, where FtsY binds SRP in a GTP-dependent manner to form a FtsY–Ffh–GTP complex. GTP hydrolysis drives conformational changes that enable the nascent chain to be transferred to the SecYEG translocon and resets the cycle for subsequent targeting events.

FtsY also interacts with acidic phospholipids in the membrane, and its activity is modulated by the lipid environment, which influences targeting efficiency. The FtsY-Ffh-SRP pathway is essential for the co-translational targeting of many membrane and secretory proteins in bacteria and is conserved across diverse species, making FtsY a key component of bacterial protein sorting. The ftsY gene encodes this receptor protein.