pH dependence of the isomerase activity of protein disulfide isomerase: insights into its functional relevance.
The isomerase efficacy of the oxidoreductase, protein disulfide isomerase (PDI), has been examined by a simple method. Using this technique, the pH-dependence of relative efficiency of isomerization reactions by PDI has been evaluated and its impact on a key structure-forming step in the oxidative folding pathway of a model protein determined. Results reveal that PDI has a greater relative impact on thiol-disulfide reshuffling (isomerization) reactions and consequently the structure-forming step in oxidative folding at pH 7, as opposed to pH's 8 and 9. These results suggest that PDI, which possesses an anomalously low thiol pKa, is fine-tuned to catalyze oxidative folding in the lumen of the endoplasmic reticulum where the ambient pH of approximately 7 would otherwise retard thioldisulfide exchange reactions and hinder acquisition of the native fold. The pH-dependent impact on isomerization catalysis has important implications for the development of synthetic chaperones for in vivo and in vitro applications.
Wang
Yu-Hsiang
YH
Department of Biological Sciences, The University of Texas at El Paso, El Paso, TX 79968, USA.
Narayan
Mahesh
M
D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D007700:Kinetics; D011487:Protein Conformation; D019704:Protein Disulfide-Isomerases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017510:Protein Folding; D012259:Ribonuclease, Pancreatic / Q000737:chemistry / Q000378:metabolism
D012259:Ribonuclease, Pancreatic; D019704:Protein Disulfide-Isomerases