Certain cell surface proteins associated with virulence are exported through the chaperone/usher pathway. They are translocated across the cytoplasmic membrane by the GSP system before binding to a periplasmic chaperone, PapD, which prevents premature folding of the peptides. Periplasmic chaperone—peptide complexes are targeted to an outer membrane protein called the usher, through which the peptide is secreted. Energy is not needed in this process. Pili are formed in this pathway (Figure 3.11).