A structural model of the SRP54 subunit of the eukaryotic signal recognition particle (SRP) reveals that a pair of cysteine residues that are almost universally conserved in the eukaryotic SRP54, but not in its prokaryotic homolog, are located on opposite surfaces of the GTPase active site. Although the two residues are too far apart to form a disulfide bond, conservation of the pair of cysteines implies strongly that they have a functional role. We hypothesize that the two residues contribute to a transient disulfide bond that modulates the function of the eukaryotic SRP GTPase.
Grant Support: NIH R21 DK 062610