BUILDING BRIDGES - DISULFIDE BOND FORMATION IN THE CELL

Disulphides are often vital for the folding and stability of proteins. Dedicated enzymatic systems have been discovered that catalyse the fo rmation of disulphides in the periplasm of prokaryotes. These discover ies provide compelling evidence for the actual catalysis of protein fo lding in vivo. Disulphide bond formation in Escherichia coil is cataly sed by at least three 'Dsb' proteins; DsbA, -B and -C. The DsbA protei n has an extremely reactive, oxidizing disulphide which it simply dona tes directly to other proteins. DsbB is required for the reoxidation o f DsbA. DsbC is active in disulphide rearrangements and appears to wor k synergistically with DsbA. The relative rarity of disulphides in cyt oplasmic proteins appears to be dependent upon a disulphide-destructio n machine. One pivotal cog in this machine is thioredoxin reductase.