Journal
BIOCHEMISTRY
Volume 42, Issue 18, Pages 5387-5394Publisher
AMER CHEMICAL SOC
DOI: 10.1021/bi026993q
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Funding
- NIGMS NIH HHS [T32 GM008505, T32 GM008505-08, GM08505] Funding Source: Medline
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Protein disulfide isomerase (PDI) utilizes the active site sequence Cys-Gly-His-Cys (CGHC; Edegrees' = -180 mV) to effect thiol-disulfide interchange during oxidative protein folding. Here, the Cys-Gly-Cys-NH2 (CGC) peptide is shown to have a disulfide reduction potential (Edegrees' = -167 mV) that is close to that of PDI. This peptide has a thiol acid dissociation constant (pK(a) = 8.7) that is lower than that of glutathione. These attributes endow the CGC peptide with substantial disulfide isomerization activity. Escherichia coli thioredoxin (Trx) utilizes the active site sequence Cys-Gly-Pro-Cys (CGPC; Edegrees' = -270 mV) to effect disulfide reduction. Removal of the proline residue from the Trx active site yields a CGC active site with a greatly destabilized disulfide bond (Edegrees' greater than or equal to -200 mV). The DeltaP34 variant retains high conformational stability and remains a substrate for thioredoxin reductase. In contrast to the reduced form of the wild-type enzyme, the reduced form of DeltaP34 Trx has disulfide isomerization activity, which is 25-fold greater than that of the CGC peptide. Thus, the rational deletion of an active site residue can bestow a new and desirable function upon an enzyme. Moreover, a CXC motif, in both a peptide and a protein, provides functional mimicry of PDI.
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