Different cation binding to the I domains of alpha 1 and alpha 2 integrins: implication of the binding site structure

In the present work, we studied the interactions of recombinant alpha l and alpha 2 integrin I domains with cations Tb3+, Mn2+, Mg2+ and Ca2+. We obse rved that alpha 1 and alpha 2 I domains bind these cations with significant ly different characteristics. The binding of Mg2+ by the alpha 1 I domain w as accompanied by significant changes of tryptophan fluorescence which coul d be interpreted as a conformational change. Comparison of the alpha 1 inte grin I domain structure obtained by comparative modeling with a known struc ture of the alpha 2 integrin I domain shows distinct differences in the met al ion binding sites which could explain the differences in cation binding. (C) 1999 Federation of European Biochemical Societies.