||"Pap fimbriae are composite structures consisting of a long, rigid base section and a short, flexible, open
helical structure (ref 78). The rigid section is composed mostly of the PapA fimbrin subunit arranged in a
tightly packed right-handed helix (Fig. 1). X-ray fiber diffraction analysis indicates that Pap fimbriae
contain 3.2 fimbrin subunits per turn of the helix and have a helical pitch of 2.4 nm (refs 25, 66). These
fimbriae are about 7 nm in diameter with a central axial hole of 1.5 nm in diameter. Since these
fimbriae usually extend about 1 to 2 µm away from the bacterial cell surface, a single rigid fiber is
composed of about 1,200 to 2,400 fimbrin monomers."