Conformational states of annexin VI in solution induced by acidic pH

Acidic pH-induced folding of annexin (Anx)VI in solution was investigated in order to study the mechanism of formation of ion channels by the protein in membranes. Using 2-(p-toluidino)naphthalene-6-sulfonic acid as a hydrophobic probe, it was demonstrated that AnxVI exerts a large change in hydrophobicity at acidic pH, Moreover, circular dichroism spectra indicated that the native state of AnxVI changes at acidic pH towards a state characterized by a significant loss of cl-helix content and appearance of new p-structures, These changes are reversible upon an increase of pH, It is postulated that the structural folding of AnxVI could explain how a soluble protein may undergo transition into a molecule able to penetrate the membrane hydrophobic region. The physiological significance of these observations is discussed. (C) 2001 Published by Elsevier Science B,V, on behalf of the Federation of European Biochemical Societies.