BINDING-AFFINITY OF PROTEINS TO HSP90 CORRELATES WITH BOTH HYDROPHOBICITY AND POSITIVE CHARGES - A SURFACE-PLASMON RESONANCE STUDY

The 90 kDa heat shock protein (hsp90) is a major cytoplasmic molecular chaperone associating with numerous other proteins including steroid receptors. Here we provide the first numerical analysis of hsp90-targe t associations using surface plasmon resonance. Binding affinities of histones, the ''native molten globule'', casein and calmodulin to hsp9 0 decrease in the order of K-d = 70 +/- 24, 220 +/- 70 and 1800 +/- 60 0 nM, respectively. Analysis of the structure of binding proteins reve aled that their binding affinity depends on both hydrophobicity and po sitive charges making the discriminative features of hsp90 similar to those of other molecular chaperones.