Calcium- and pH-linked oligomerization of sorcin causing translocation from cytosol to membranes

Sorcin, a cytosolic calcium-binding protein containing a pair of EF-hand motifs, undergoes a Ca2(+)-dependent translocation to the cell membrane. The underlying conformational change is similar at pH 6.0 and 7.5 and consists in an increase in overall hydrophobicity that involves the aromatic residues and in particular the two tryptophan residues which become less exposed to solvent. The concomitant association from dimers to tetramers indicates that the tryptophan residues, which are located between the EF-hand sites, become buried at the dimer-dimer interface. Ca2(+)-bound sorcin displays a striking difference in solubility as a function of pH that has been ascribed to the formation of calcium-stabilized aggregates.