Degradative signals in the annexins

Annexins are a superfamily of calcium-dependent membrane-associated proteins which interact with phospholipids [1]. The primary structure of Annexins I and III contain a region enriched in proline, glutamate, serine and threonine (PEST sequences) towards the N-tarminal and. These sequences are believed to be the signals for rapid intercellular degradation. Annexin I is known to be cleaved by calpain near its PEST region and this would suggest that the PEST 'region in Annexin I is a possible calpain recognition site. Annexins II, V and VI also possess PEST regions somewhat distal to the N-terminus. We have found that eight of the tan known mammalian Annexins contain a pentapeptide sequence that is biochemically related to the KFERQ motif which is believed to be the signal that targets protein for lysosomal proteolysis. Our data suggest that the annexins could be degraded by lysosomal proteolysis and could also be regulated by limited proteolysis.