Modified annexin proteins, including a homodimer of human annexin V, are provided. Methods for their use, such as to prevent thrombosis without increasing hemorrhage, enhancing the survivability of platelets during storage or transfusion and to attenuate ischemia-reperfusion injury (IPI), are also provided. The modified annexins bind phosphatidylserine (PS) on cell surfaces, thereby preventing the assembly of the prothrombinase complex. The modified annexin decreases the binding of leukocytes and platelets during post-ischemic reperfusion, thereby restoring microvascular blood flow and decreasing organ damage. In addition, the modified annexin prevents lipid loss from platelets during storage.