Signal recognition particle

  • OMIM: 600 708
  • UniProt: P37108
  • OMIM: 182 175
  • UniProt: P09132
  • OMIM: 604 857
  • UniProt: P61011
  • OMIM: 604 858
  • UniProt: Q9UHB9
  • OMIM: 602122
  • UniProt: O76094

The signal recognition particle (English signal recognition particle SRP) is a ribonucleoprotein, which is involved in the co-translational transport of proteins into the endoplasmic reticulum in eukaryotes and the plasma membrane of prokaryotes.

The core of the SRP is universal and conserved in all six biological kingdoms.

Construction

Components

SRP has a different composition in eukaryotes and prokaryotes, but has some similarities. For eukaryotes, SRP is the best studied of mammals. He consists of a 300 nucleotide long, usually double- 7SL RNA and six polypeptides with a mass of 9, 14, 19, 54, 68 and 72 kDa. They are therefore also called SRP9, SRP14, SRP19, SRP54, SRP68 and SRP72 called. In the baker's yeast Saccharomyces cerevisiae, a unicellular eukaryote, the RNA (SCR1 ) has a sedimentation coefficient of 11S. The proteins are homologous to those in mammals and carry the designation Srp21p, Srp14p, Sec65p, Srp54p, Srp68p and Spr72p. Other primitive eukaryotes such as Giardia intestinalis or the protozoa Trypanosoma cruzi lacks the homologs of SRP9 and SRP14. The parasite Encephalitozoon cuniculi also lacks a homolog SRP68 and SRP72.

Prokaryotes have a much smaller SRP. In some Gram positive bacteria such as Bacillus subtilis RNA ( scRNA ) 6S is large, while the sedimentation of the SRP - RNA ( FFS) in Gram-negative bacterium Escherichia coli 4.5 s, and it has a length of 114 nucleotides. Bacteria have only one homolog SRP54, which ( fiftyfour - homologous English for " 54 homolog " ) is called Ffh. In B. subtilis associated additionally a 10 kDa protein HBSu with the SRP - RNA.

SRP19 and SRP54. Archaea in the 7S RNA of eukaryotes, but these only two homologs of SRP proteins on similar Plants possess not only a cytosolic SRP SRP also in the chloroplasts. This consists of a SRP54 - homologous protein ( cpSRP54 ) and cpSRP43, a 43 kDa protein. Plastid SRP is unique because it has no RNA.

Structure

SRP consists of a S- and an aluminum domain that reflect the two different functions of the complex. The S- domain in eukaryotes from SRP54, SRP19, the Hetereodimer SRP68/SRP72, and three helices of SRP RNA ( helix 6-8) put together. In bacteria, only the helix 8 and the SRP54 homolog Ffh are conserved, while in the archaea homolog SRP54 and SRP19 are obtained. There, however, lacks the helix 7 S domain mediates the binding to the signal sequence of a protein and to the SRP- receptor to the membrane of the ER.

The Alu domain is composed in eukaryotes from the Hetereodimer SRP9/14 and the rest of the SRP RNA. There you will also find the 5 'and the 3' end of the RNA. The aluminum domain is responsible for a delay during translation. Since this domain is missing in many bacteria there such a translational delay is unlikely. In addition, data from the cryo-electron microscopy indicated that SRP is bound by the Alu domain of the small ribosomal subunit ( 40S ).

Importance

The complex has GTPase activity. The recognition of the signal peptide, consisting of at least 8 non-polar amino acids in the center is performed in the GTP- bound state. As it leaves the ribosomal channel, it is detected by the SRP54 subunit.

The SRP complex is present in eukaryotes in the cytosol. It binds reversibly to the signal sequence of the translated protein and especially the large subunit of the ribosome. The signal sequence has a length of 15 to 50 amino acids and consists of a positively charged N-terminal region and a polar C-terminal region.

The translation of the protein is delayed and the entire complex of polypeptide SRP and ribosome binds to an SRP receptor in the endoplasmic reticulum. A translocation ( translocon ) already present amino acid chain is converted into the lumen of the ER. The SRP and its receptor during which hydrolyze GTP to GDP and dissociate. The translation is then continued.

History

The SRP was identified and characterized by Peter Walter, when he worked as a graduate student under Günter Blobel.

Human Genome Organisation Signal recognition particle RNA Giardia lamblia Signal recognition particle receptor G-Protein Hydrolysis Digital Object Identifier
729726
de