PEST SEQUENCES IN EF-HAND CALCIUM-BINDING PROTEINS

Calcium binding proteins are subdivided into two major families: the E F-hand family and the Annexin family. The EF-hand family is distinguis hed by the characteristic helix-loop-helix motif which consists of two alpha-helices separated by a loop. The EF-hand Ca2+-binding protein f amily contain subfamilies rich in proline, glutamic acid, serine and t hreonine residues (called PEST sequences) and non PEST-containing subf amilies. A few of the Ca2+-binding proteins contain KFERQ-like sequenc es which are thought to be possible signals for lysosomal degradation. Arginine pairs (RR) which have also been suggested to act as signals for proteolysis were found to be few or absent. However, most EF-hand proteins were found to possess lysine pairs (KK) which may also act as signals for proteolysis.