Binding of lysozyme to common pili of Escherichia coli

Common pili from Escherichia coli were found to bind hen egg white lysozyme. The binding was highly dependent on ionic strength, and the maximum binding occurred near an ionic strength of 0.02. The pili were aggregated by lysozyme, and this process could be followed by optical turbidity, electron microscopy, and coprecipitation. Near the maximum saturation of binding, one lysozyme molecule was bound by two pilus protein subunits. Electron micrographs of this aggregate indicated that they were paracrystalline structures. Piliated bacteria were more readily agglutinated by lysozyme than were nonpiliated bacteria. Since lysozyme is considered to be an antibacterial humoral factor and since pili are considered to be a colonization factor, the binding of lysozyme may represent an important bacterium-host interaction