Cooperation between Subunits Is Essential for High-Affinity Binding of N-Acetyl-D-hexosamines to Dimeric Soluble and Dimeric Cellular Forms of Human CD69
2010
Abstract
CD69 is an earliest lymphocyte activation antigen and a universal leukocyte triggering molecule expressed at sites of active immune response. The binding of GlcNAc to the dimeric human CD69 was followed by equilibrium dialysis, fluorescence titration, and NMR.
Clear cooperation was observed in the high-affinity binding (Kd=4.0 X 10-7 M) of the carbohydrate to two subunits of the dimeric CD69 (Hill coefficient 1.94). A control monosaccharide ManNAc was not bound by human CD69, and both monosaccharides had no effects on the structure of the receptor.
However, a monomeric CD69 obtained by mutating Q93 and R134 at the dimer interface exhibited a much lower affinity for GlcNAc (Kd=1.3 X 10-5 M) and no cooperativity (Hill coefficient 1.07).