Protein folding endoplasmic reticulum

In addition to folding as a single-chain heterodimer, the HAj—HA2 complex undergoes transient associations with other proteins, namely chaperones, followed by a more permanent self-association, in its endoplasmic reticulum (ER) folding environment. It need not be supposed that chaperones actively induce folding of HA into a metastable... 

For shotgnn-LC-MS identification, selective prefractionation by means of AfC is a powerful tool. Biotinylation of cell-surface proteins and subsequent streptavidin-AfC enabled a 1600-fold and 400-fold emichment of plasma membrane proteins over proteins from mitochondria and endoplasmic reticulum, respectively [78-79]. Because of the selective isolation procedure, only 3% of the 918 unique proteins identified were related to mitochondria and endoplasmic reticulum proteins, and 25% were either plasma membrane proteins or membrane-associated proteins. 

Braakman, I., Helenius, J., and Helenius, A. (1992). Manipulating disulfide bond formation and protein folding in the endoplasmic reticulum. EMBO J. 11, 1717—1722. 

Harding, H. P., Zhang, Y., and Ron, D. (1999). Protein translation and folding are coupled by an endoplasmic—reticulum-resident kinase. Nature 397, 271—274. 

The endoplasmic reticulum (ER) is responsible for the production of the protein and lipid components of most of the cell s organelles. The ER contains a large number of folds, but the membrane forms a single sheet enclosing a single closed sac. This internal space is called the ER lumen. The smooth endoplasmic reticulum (ER) in muscle cells contains the vesicles and tubules that serve as a store of calcium ions. These are released as one step in the muscle contraction process. Calcium pumps, Ca +-ATPases, serve to move the calcium from the cytoplasm to the ER or SR lumen. 

Inhibits protein synthesis by interfering with endoplasmic reticulum and Golgi apparatus functions it also induces cell differentiation and caspase-dependent apoptosis Stabilizes protein structures and restores correct folding tiirough binding with tiiem... 

Knittler MR, Dirks S, Haas IG (1995) Molecular chaperones involved in protein degradation in the endoplasmic reticulum quantitative interaction of the heat shock cognate protein BiP with partially folded immunoglobulin light chains that are degraded in the endoplasmic reticulum. Proc Natl Acad Sd USA 92 1764-1768... 

They may enter the cytosol and fold quickly into a compact form. This may require only a few seconds, whereas the translation process in the ribosome may take many seconds. The folding will therefore be cotranslational.525 Depending upon the N-terminal signal peptide the protein may later unfold and pass through a membrane pore or translocon into the endoplasmic reticulum (ER), a mitochondrion, chloro-plast, or peroxisome. Wherever it is, it will be crowded together with thousands of other proteins. It will interact with many of these, and evolution will have enabled some of these to become chaperones (discussed in Chapter 10).526... 

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