Proteins that are retained in the Endoplasmic Reticulum, or ER, after folding are known as ER resident proteins. Their localization to the ER often depends on certain sequences of amino acids located at the N-terminal or C-terminal. The classical ER retention signal is the C-terminal KDEL sequence. These signals allow for retrieval from the Golgi apparatus, effectively maintaining the protein in the ER. Other mechanisms for ER retention are being studied but are not as well characterized as signal retention. The endoplasmic reticulum or ER (endoplasmic means within the cytoplasm, reticulum means little net) is an organelle found in all eukaryotic cells. ... Protein folding is the process by which a protein structure assumes its functional shape or conformation. ... In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups. ... The N-terminal end refers to the extremity of a protein or polypeptide terminated by an amino acid with a free amine group (NH2). ... The C-terminal end refers to the extremity of a protein or polypeptide terminated by an amino acid with a free carboxyl group (COOH). ... In cell biology, the Golgi apparatus (also called a Golgi body, Golgi complex, or dictyosome) is an organelle found in most eukaryotic cells, including those of plants, animals, and fungi. ...
Proteins that reside in the lumen of the ER are characterized by a C-terminal signal that prevents their passage along the secretory pathway (for review see Pelham, 1989).
Proteins bearing this retention signal are able to leave the ER by vesicular transport but are specifically retrieved from the Golgi or a pre-Goigi "salvage" compartment.
Retention of the HDEL construct was improved, but in addition partial retention of both DDEL and KDEL was observed (Figure 4B).
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