THE C-TERMINAL DOMAIN OF THE SECRETIN PULD CONTAINS THE BINDING-SITE FOR ITS COGNATE CHAPERONE, PULS, AND CONFERS PULS DEPENDENCE ON PLV(F1) FUNCTION

Related outer membrane proteins, termed secretins, participate in the secretion of macromolecules across the outer membrane of many Gram-neg ative bacteria. In the pullulanase-secretion system, PulS, an outer me mbrane-associated lipoprotein, is required both for the integrity and the proper outer membrane localization of the PulD secretin. Here we s how that the PulS-binding site is located within the C-terminal 65 res idues of PulD. Addition of this domain to the filamentous phage secret in, plV, or to the unrelated maltose-binding protein rendered both pro teins dependent on PulS for stability. A chimeric protein composed of bacteriophage f1 plV and the C-terminal domain of PulD required proper ly localized PuIS to support phage assembly. An in vivo complex formed between the plV-PulD(65) chimera and PulS was detected by co-immunopr ecipitation and by affinity chromatography.