Heterodimeric interaction and interfaces of S100A1 and S100P

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Abstract

With the widespread use of yeast two-hybrid systems, many heterodimeric forms of S100 proteins have been found, although their biological significance is unknown. In the present study, S100Al was found to interact with another S 100 protein, S100P, by using the yeast two-hybrid system. The binding parameters of the interaction were obtained using an optical biosensor and show that S100P has a slightly higher affinity for S100Al (K-d = 10-20 nM) when compared with that for self-association (K-d = 40-120W). The physical interaction of S100Al and S100P was also demonstrated in living mammalian cells using a fluorescence resonance energy transfer technique. Preincubation of recombinant S100P with S100Al, before the biosensor assay, reduced by up to 50 % the binding of S100P to a recombinant C-terminal fragment of non-muscle myosin A, one of its target molecules. Site-specific mutations of S100P and S100Al, combined with homology modelling of an S100P/S100Al heterodimer using known S100P and S100Al structures, allowed the hydrophobic interactions at the dimeric interface of the heterodimer to be defined and provide an explanation for the heterodimerization of S100P and S100Al at the molecular level. These results have revealed the similarities and the differences between the S100P homodimer and the S100Al/S100P heterodimer.

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