K99 surface haemagglutinin of enterotoxigenic E. coli recognize terminal N-acetylgalactosamine and sialic acid residues of glycophorin and other complex glycoconjugates.

The possible nature of the erythrocyte receptor for K99 haemagglutinin is described. The receptor is a glycophorin which possesses NANA alpha 2-6 GalNAc structures for which this haemagglutinin has a strong affinity. Human, porcine and equine erythrocytes which are haemagglutinated by K99 all have similar glycophorin oligosaccharide structures. K99 has affinity for both NANA and GalNAc at terminal positions, but the affinity for alpha 2-6-linked NANA is higher than for alpha 2-8-linked NANA.