ANNEXINS POSSESS FUNCTIONALLY DISTINGUISHABLE CA2-BINDING DOMAINS( AND PHOSPHOLIPID)

All annexins bind Ca2+ and phospholipids, although individual annexins differ markedly in their affinities for these ligands. Annexin I bind s phosphatidylserine (PS) at lower [Ca2+] than annexin V,while annexin V exhibits a higher affinity for PS than does annexin I. To identify the structural determinants of these properties, we characterized a se ries of chimeric annexins. A chimera containing repeat 1 of annexin V fused to repeats 2, 3, and 4 of annexin I exhibited a Ca2+ requirement for PS binding close to that of annexin I, while chimeras containing repeat 1 of annexin I fused to repeats 2, 3, and 4 of annexin V requir ed higher [Ca2+], similar to that of annexin V. In contrast, the overa ll affinity for PS vesicles was determined by the source of repeat 1. The chimera that contained repeat 1 of annexin V exhibited a high affi nity for PS, while a chimera that contained repeat 1 of annexin I had a low affinity for PS similar to that of annexin I. We conclude that t he [Ca2+] requirement for phospholipid binding and the overall phospho lipid affinity of annexins are determined by distinct domains. (C) 199 4 Academic Press, Inc.