ABSTRACT
For a long time it has been debated whether secreted proteins need the assistance of molecular chaperones in the periplasm, as newly synthesized polypeptides emerging from the ribosomes do (Hartl, 1996; Hendrick and Hartl, 1993; Welch et al., this volume). The periplasmic space of gram-negative bacteria provides a special environment for protein folding for several reasons. First, it favors the oxidation of disulfide bonds, second it lacks ATP, a component essential for the activity of most cytoplasmic chaperones. The question whether periplasmic chaperones exist and associate with nascent polypeptides emerging at the translocation sites is related to the question of how these polypeptides can be protected against the attack by the many proteases which can rapidly degrade slow-folding newly translocated species. The DegP/HtrA protease in particular has been shown to degrade abnormal secreted polypeptides (Strauch and Beckwith, 1988) and its own synthesis is induced by stress, including elevated temperature (Lipinska et al., 1989).
