Screening and Selection Strategies for Disulfide Isomerase Activity

Disulfide isomerases (EC 5.3.4.1) were first discovered almost 40 years ago by Christian Anfinsen, and have since been shown to occur in numerous organisms from bacteria to man (1 ). These enzymes play a key role in disulfide bond formation, an essential step in the oxidative folding of secreted proteins. The effort to determine the in vivo function and substrate specificity of disulfide isomerases has been hampered by the fact that, in vitro, the same isomerase enzyme can catalyze protein thiol oxidation, disulfide bond reduction, or disulfide bond rearrangement depending upon the redox conditions (2 ). Despite decades of studies, the detailed catalytic mechanism of disulfide bond isomerization is still not completely understood.