PROTEIN DISULFIDE-ISOMERASE - BUILDING BRIDGES IN PROTEIN-FOLDING

Protein disulphide isomerase (PDI) has been known for many years to as sist in the folding of proteins containing disulphide bonds, but the e xact mechanism by which it achieves this is only now becoming clear. T he active site of PDI closely resembles that of the redox protein thio redoxin, and cDNA cloning has revealed a superfamily of proteins with related active-site sequences, in organisms ranging from bacteria to h igher animals and plants. Recent mutagenesis studies are now helping t o unravel the catalytic mechanism of PDI, and work in yeast and other systems is clarifying the physiological roles of the multiple PDI-rela ted proteins.