Human S100A5 binds Ca2+ and Cu2+ independently.

S100A5 can bind Ca2+ and Cu2+ ions simultaneously and independently. This observation is in direct contrast to previously-reported antagonism between binding of Cu2+ and Ca2+ ions. The previous result is likely due to metal-dependent aggregation. Little is known about the biology of S100A5, so an accurate understanding of the biochemistry is necessary to make informed biological hypotheses. Our observations suggest the possibility of independent biological functions for Cu2+ and Ca2+ binding by S100A5.