Cooperativity weak binding /high affinity

The B pentamer of CT (CTB) interacts with the soluble, monovalent oligosaccharide portion of GMl (GMl-os) with strong affinity, the binding process is weakly cooperative. The dissociation constant for the monovalent interaction of one GMl-os with one B pentamer binding site has been evaluated by ITC and found to be 43 nM [11], the highest affinity for a carbohydrate-protein interaction described to date. On cell membranes, this initial binding event is further amplified by the multivalent interaction of the Bj pentamer with multiple copies of GMl-os presented at high concentration in lipids rafts at the cell surface [29]. 

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