CALCIUM-LINKED AND PH-LINKED OLIGOMERIZATION OF SORCIN CAUSING TRANSLOCATION FROM CYTOSOL TO MEMBRANES

Sorcin, a cytosolic calcium-binding protein containing a pair of EF-ha nd motifs, undergoes a Ca2+-dependent translocation to the cell membra ne, The underlying conformational change is similar at pH 6.0 and 7.5 and consists in an increase in overall hydrophobicity that involves th e aromatic residues and in particular the two tryptophan residues whic h become less exposed to solvent, The concomitant association from dim ers to tetramers indicates that the tryptophan residues, which are loc ated between the EF-hand sites, become buried at the dimer-dimer inter face, Ca2+-bound sorcin displays a striking difference in solubility a s a function of pH that has been ascribed to the formation of calcium- stabilized aggregates. (C) 1997 Federation of European Biochemical Soc ieties.