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Lodish H, Berk A, Zipursky SL, et al. Molecular Cell Biology. 4th edition. New York: W. H. Freeman; 2000.

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Molecular Cell Biology. 4th edition.

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Figure 17-26. (a) Rearrangement of disulfide bonds by protein disulfide isomerase (PDI).

Figure 17-26(a) Rearrangement of disulfide bonds by protein disulfide isomerase (PDI)

PDI contains an active-site with two reduced cysteine sulfhydryl (–SH) groups. The ionized (–S) form of one of these groups reacts with disulfide (S – S) bonds on nascent or newly completed proteins to form a disulfide-bonded PDI-substrate protein intermediate. This generates a free –S group on the protein, which, in turn, can react with another disulfide bond in the protein to form a new disulfide bond and another free –S group. In this way, the disulfide bonds on a protein can rearrange themselves until the most stable conformation for the protein is achieved, and free PDI is released. (b) An escape hatch for PDI. Occasionally PDI forms a disulfide bond with a protein that is irreversibly misfolded. PDI eventually escapes when the second –S group in the active site attacks the disulfide bond between PDI and the protein, releasing PDI with an internal (intramolecular) disulfide bond. [Part (a) after R. B. Freedman, 1984, Trends Biochem. Sci. 9:438, and R. Noiva and W. Lennarz, 1992, J. Biol. Chem. 267:3553. Part (b) after K. Walker et al., 1997, J. Biol. Chem. 272:8845.]


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