CELL BIOLOGY: Push Me-Pull You

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Science  07 Jul 2006:
Vol. 313, Issue 5783, pp. 19b
DOI: 10.1126/science.313.5783.19b

Proteins destined for secretion or for the cell surface are synthesized and cotranslationally inserted at the endoplasmic reticulum (ER). After entering the ER, proteins are guided to fold properly by chaperones such as protein disulfide isomerase (PDI). Sometimes, however, misfolding occurs, and under these circumstances, an elaborate process of quality control is set into motion. Misfolded proteins are either retained in the ER or retrotranslocated back into the cytosol for degradation by the proteasome; in both cases they are prevented from transiting further through the secretory pathway. Forster et al. have looked at the passage from the ER into the cytosol of cholera toxin, which cleverly travels via the retrotranslocation machinery. PDI promoted cholera toxin retrotranslocation, but the PDI-like protein p72 promoted ER retention. These two proteins both altered the conformation of cholera toxin to achieve the respective outcomes. Furthermore, this pair played a similar push me-pull you game with misfolded endogenous ER proteins. — SMH

J. Cell Biol. 173, 853 (2006).

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