Different cation binding to the I domains of alpha1 and alpha2 integrins: implication of the binding site structure

In the present work, we studied the interactions of recombinant alpha1 and alpha2 integrin I domains with cations Tb(3+), Mn(2+), Mg(2+) and Ca(2+). We observed that alpha1 and alpha2 I domains bind these cations with significantly different characteristics. The binding of Mg(2+) by the alpha1 I domain was accompanied by significant changes of tryptophan fluorescence which could be interpreted as a conformational change. Comparison of the alpha1 integrin I domain structure obtained by comparative modeling with a known structure of the alpha2 integrin I domain shows distinct differences in the metal ion binding sites which could explain the differences in cation binding.