N-terminus of mature heat-labile enterotoxin chain B is critical for its extracellular secretion in Vibrio cholerae

The effects of addition of a few amino acids to the amino- and carboxy-term inal regions of the mature portion of the heat-labile enterotoxin chain B ( LTB) of Escherichia coli on protein export, secretion and assembly were inv estigated. In E. coli, LTB (secretory protein) with or without the extensio n at the N- or C-terminus accumulated in the periplasmic fraction. For Vibr io choler ne, LTB with the extension at the C-terminus was exported to the periplasm followed by secretion to the extracellular milieu, However, LTB w ith the N-terminus extension was exported to the periplasm only. Our findin gs suggest that in the case of V. cholerae, the N-terminus of the mature LT B plays an important role in its secretion to the extracellular milieu. (C) 1999 Federation of European Biochemical Societies.