Cotranslational folding - omnia mea mecum porto?

Evidence for cotranslational folding on both prokaryotic and eukaryotic rib osomes is reviewed. Molecular chaperones appear to assist only in a small f raction of newly synthesized proteins in folding into their native conforma tion. the recently published crystal structure of the large ribosomal subun it at 2.5 Angstrom resolution has provided the basis for understanding wher e and how peptide synthesis takes place on the ribosome. The nascent peptid e is concluded to pass through a tunnel that extends about 100 Angstrom bet ween the peptidyl transferase center and its exit site. The minimum diamete r of the tunnel and the apparent physical and chemical properties of its wa lls appear to preclude complex folding of the nascent peptides that are pro tected within the ribosomes vary in length from about 30 to 72 amino acid r esidues. This suggests that nascent peptides have different conformations. It is hypothesized that folding of the nascent polypeptide into its native conformation starts in the distal portion of the tunnel, and proceeds at th e surface of the ribosomal subunit in a depression or bay near the exit ope ning of the tunnel. (C) 2001 Elsevier Science Ltd. All rights reserved.