Repeated PapE subunits make up the thin (2 nm in diameter) tip fibrillum of the P pilus. Subunits are arranged in a open helical conformation. Pili with a defective papE gene have low adhesive capacity or none; however, the binding property of the whole cell is not affected. Pili are polar filaments radiating from the surface of the bacterium to a length of 0.5-1.5 micrometers and numbering 100-300 per cell, and enable bacteria to colonize the epithelium of specific host organs. Probably interacts with chaperone PapD. Assembly of the P pilus requires periplasmic chaperone PapD, in absence of the chaperone overexpression of this subunit is toxic, with PapE accumulating in the periplasm (PubMed:9351822). Misfolded protein interacts with CpxP, which probably targets it for degradation (PubMed:25207645). At the tip of the P pilus. Overexpression of this protein in the absence of chaperone PapD leads to proteolysis of itself and CpxP; degradation requires both cpxP and degP, as well as the N-terminus of PapE (PubMed:16303867). Strains of E.coli that cause infection of the human urinary tract produce pap-pili (P pili) which are hair-like appendages consisting of about 1000 helically arranged subunits of the protein PapA. These pili mediate binding to digalactoside-containing glycolipids present on the epithelial cells which line the urinary tract.