N-terminal helices and A domain of archaeal FtsY facilitate SRP54 binding and the association with cell membrane

Abstract

AbstractThe process of protein translocation is essential to the maintenance of cellular life and has been critically addressed in eukaryotes and bacteria. However, little information is available regarding protein translocation across archaeal membranes. The signal recognition particle (SRP) plays an important role in this process. It binds the signal peptide at the N-terminus of the polypeptide chain and interacts with the cognate SRP receptor (FtsY) located on the target membrane to form a targeting complex (TC). Concomitant GTP hydrolysis by SRP and FtsY delivers the polypeptide to the adjacent protein-conducting channel. The present study aims to characterize the structural domains of FtsY contributing to the targeting complex (TC) formation in Sulfolobus acidocaldarius, a thermo-acidophilic crenarchaeon. The contacting residues between SRP54 and FtsY were mapped along the αN1-N3 helices. Interestingly, the previously reported crystal structure did not take the N-terminal A domain into account – a region rich in negatively charged residues. Such observation led us to investigate the contribution of each of the three participating helices (αN1-3) in terms of membrane association and functional TC formation. Through biophysical analyses of SRP-FtsY and FtsY-membrane interaction, and biochemical characterization of the reciprocal GTPase activity, this work sought to elucidate the minimal structural motif controlling the archaeal TC assembly.