Abstract

All cells have the ability to synthesize and secrete proteins. Although many details of this process are well-known, Martin Kampmann and Günter Blobel recently highlighted two “landmark papers” that used cryo-electron microscopy (cryoEM) to obtain information at subnanometer resolution, which provided direct visualization of nascent polypeptide chains in the tunnel with ribosomes . It is known that the signal peptide (the first few amino acids on the amino terminal that do not become part of the final polypeptide) emerges from a ribosome and engages the signal recognition particle (SRP) in the cytoplasm, and this complex is directed to the SRP receptor on the endoplasmic reticulum (ER). The SRP is released, the signal peptide enters the protein-conducting channel (PCC), and the nascent polypeptide chain (that will become the protein) enters the lumen of the ER.

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