The PapG adhesin of uropathogenic Escherichia coli contains separate regions for receptor binding and for the incorporation into the pilus.

Most uropathogenic strains of Escherichia coli produce heteropolymeric organelles, known as P pili, that bind to the globoseries of glycolipids present in the urinary tract. The formation of a P pilus is the result of a family of related proteins being coordinately assembled into the structure in a defined order with the adhesin located exclusively at the tip. The preassembled digalactoside alpha-D-galactopyranosyl-(1----4)-beta-D-galactopyranose-binding adhesin was purified to homogeneity from the periplasmic space in a complex with the periplasmic assembly protein PapD by affinity chromatography to alpha-D-galactopyranosyl-(1----4)-beta-D-galactopyranose-Sepharose. A receptor-binding domain was mapped to the amino-terminal half of the adhesin. The interaction of PapD with PapG, which was required for the incorporation of the adhesin into the pilus, was found to protect PapG from proteolytic cleavages and enhanced the processing of the PapG signal peptide. A preassembly domain necessary for forming a complex with PapD was mapped to the carboxyl terminus of PapG.