THE REQUIREMENT FOR DSBA IN PULLULANASE SECRETION IS INDEPENDENT OF DISULFIDE BOND FORMATION IN THE ENZYME

Results from previous studies have suggested that an intramolecular di sulphide bond in the exoprotein pullulanase is needed for its recognit ion and transport across the outer membrane. This interpretation of th e data is shown here to be incorrect: pullulanase devoid of all potent ial disulphide bonds is secreted with apparently the same efficiency a s the wild-type protein. Furthermore, the periplasmic disulphide bond, oxido-reductase DsbA, previously shown to catalyse the formation of a disulphide bond in pullulanase and to decrease its transit time in th e periplasm, is shown here to be required for the rapid secretion of p ullulanase devoid of disulphide bonds. Several possible explanations f or the role of DsbA in pullulanase secretion are discussed.