InterPro domain: IPR042101

The signal recognition particle (SRP) is a ribonucleoprotein that mediates co-translational targeting of nascent proteins to the membrane. SRP54 of the signal recognition particle has a three-domain structure: an N-terminal helical bundle domain, a GTPase domain, and the M-domain that binds the 7s RNA and also binds the signal sequence. The extreme C-terminal region is glycine-rich and lower in complexity and poorly conserved between species.

This superfamily describes the N-terminal domain, a four-helical bundle, that has a key function in regulating the nucleotide-binding interactions of the GTPase domain. The SRP54 component is a GTP-binding protein that interacts with the signal sequence when it emerges from the ribosome [ 1 ].

1. Structural basis for mobility in the 1.1 A crystal structure of the NG domain of Thermus aquaticus Ffh. J. Mol. Biol. 320, 783-99