There has been a recent resurgence of interest in the post-translation
al modification of serine and threonine hydroxyl groups by glycosylati
on, because the resulting O-linked oligosaccharide chains tend to be c
lustered over short stretches of peptide and hence they can present mu
ltivalent carbohydrate antigenic or functional determinants for antibo
dy recognition, mammalian cell adhesion and microorganism binding. Co-
operativity can greatly increase the affinity of interactions with ant
ibodies or carbohydrate binding proteins. Thus, in addition to their k
nown importance in bearing tumour associated antigens in the gastroint
estinal and respiratory tracts, glycoproteins with O-linked chains hav
e been implicated as ligands or co-receptors for selectins (mammalian
carbohydrate binding proteins). Microorganisms may have adopted simila
r mechanisms for interactions with mammalian cells in infection, by ha
ving relatively low affinity ligands (adhesins) for carbohydrate bindi
ng, which may bind with higher affinity due to the multivalency of the
host ligand and which are complemented by other virulence factors suc
h as interactions with integrin-type molecules. In addition to specifi
c adhesion signals from O-linked carbohydrate chains, multivalent O-gl
ycosylation is involved in determining protein conformation and formin
g conjugate oligosaccharide-protein antigenic, and possible functional
determinants.