Publication Abstract from PubMed
Protein translocation across and insertion into membranes is essential to all life forms. Signal peptide-bearing nascent polypeptide chains emerging from the ribosome are first sampled by the signal-recognition particle (SRP), then targeted to the membrane via the SRP receptor (SR), and, finally, transferred to the protein-conducting channel. In eukaryotes, this process is tightly controlled by the concerted action of three G proteins, the 54-kD subunit of SRP and the alpha- and beta-subunits of SR. We have determined the 2.2-A crystal structure of the nucleotide-free SRbeta domain. Unexpectedly, the structure is a homodimer with a highly intertwined interface made up of residues from the switch regions of the G domain. The remodeling of the switch regions does not resemble any of the known G protein switch mechanisms. Biochemical analysis confirms homodimerization in vitro, which is incompatible with SRalpha binding. The switch mechanism involves cis/trans isomerization of a strictly conserved proline, potentially implying a new layer of regulation of cotranslational transport.
Homodimerization of the G protein SRbeta in the nucleotide-free state involves proline cis/trans isomerization in the switch II region.,Schwartz TU, Schmidt D, Brohawn SG, Blobel G Proc Natl Acad Sci U S A. 2006 May 2;103(18):6823-8. Epub 2006 Apr 20. PMID:16627619[1]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
