Recent advances in the mechanism of the SRP GTPase regulation

Co-translational targeting of proteins destined for membrane integration or secretion is mediated by the universally conserved signal recognition particle (SRP) and its receptor (SR) [1]. SRP is a ribonucleoprotein complex and binds to hydrophobic signal sequences of nascent polypeptide chains as they emerge from ribosomal exit tunnel. The SRP/RNC (ribosome nascent chain) complex interacts with the membrane associated SR. The delivery of the RNC to the translocation channel in the membrane leads to dissociation of the SRP/SR complex. In order to coordinate the presence of a signal sequence at the ribosome with the availability of a vacant translocation channel, two GTPases present in SRP and SR form a unique complex in which GTP hydrolysis is activated in a composite active site. Progress towards the mechanism of SRP GTPase activation will be presented.