1NRJ: Signal Recognition Particle Receptor Beta-subunit In Complex With The Srx Domain From The Alpha-subunit

Protein translocation across and insertion into membranes is a process essential to all life forms. In higher eukaryotes, this process is initiated by targeting the translating ribosome to the endoplasmic reticulum via the signal recognition particle (SRP) and its membrane-associated heterodimeric receptor (SR). This targeting step is regulated by three G proteins, SRP54, SR alpha, and SR beta, which act in concert. Little is known about the regulatory role of SR beta. Here, we present the 1.7 A crystal structure of the SR beta-GTP subunit in complex with the interaction domain of SR alpha. Strikingly, the binding interface overlaps largely with the switch 1 region of SR beta. This finding, together with additional biochemical data, shows that the eukaryotic SR is a conditional and not an obligate heterodimer. The results suggest that the GTP/GDP switch cycle of SR beta functions as a regulatory switch for the receptor dimerization. We discuss the implications for the translocation pathway.
PDB ID: 1NRJDownload
MMDB ID: 22431
PDB Deposition Date: 2003/1/24
Updated in MMDB: 2017/11
Experimental Method:
x-ray diffraction
Resolution: 1.7  Å
Source Organism:
Similar Structures:
Biological Unit for 1NRJ: dimeric; determined by author and by software (PISA)
Molecular Components in 1NRJ
Label Count Molecule
Proteins (2 molecules)
Signal Recognition Particle Receptor Alpha Subunit Homolog(Gene symbol: SRP101)
Molecule annotation
Signal Recognition Particle Receptor Beta Subunit(Gene symbol: SRP102)
Molecule annotation
Chemicals (4 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB