A Thermodynamic Study of the Binding of the E. coli F41 Adhesin to its Receptor, Human Glycophorin
Colonisation by many types of bacteria is known to depend upon their ability to adhere to host cells via protein surface appendages known as adhesins. Although the structures of few adhesins are known, they have frequently been thought to be associated with long helical coils of a relatively low molecular weight subunit which form linear appendages known as pili or fimbriae. Pili may reach lengths of a micron or more and are readily visible in EM images of the bacteria which bear them. Not all adhesins are associated with such structures, however, and non-linear, afimbrial adhesins whose geometry has not been studied but which also contain many copies of a subunit polypeptide have been described. In a number of cases, bacteria are known to bind to specific structures on the host surface via their adhesins. Detailed studies on adhesin-receptor interactions are few, however, and no molecular binding studies have been reported to date. Although adhesion to host cells is often associated with the presence of pili or afimbrial aggregates, there is little evidence relevant to the actual location of the binding sites for receptors. Genetic manipulation of some E. coli strains has shown, in fact, that the binding sites are not located on the pilin monomer, but occur on a protein present in much lower concentration whose physical relationship to the pili is unknown. In other systems there is evidence that adhesion occurs only at the tip of the pili. Only in one case of gonnocal pili have results been obtained which indicate that the adhesion binding site is located on a pilin monomer, and in this case the receptor was not known.