Open AccessStructural and functional characterization of endonexin II, a calcium- and phospholipid-binding protein.
Author(s) -
David D. Schlaepfer,
Tevie Mehlman,
Wilson H. Burgess,
Harry T. Haigler
Publication year - 1987
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.84.17.6078
Subject(s) - phosphatidylserine , phosphatidylethanolamine , peptide sequence , phospholipid , biochemistry , biology , egta , binding protein , binding site , calcium , chemistry , phosphatidylcholine , membrane , organic chemistry , gene
A protein with an apparent Mr of 33,000 was previously purified from the EGTA eluate of a human placental particulate fraction. We now report the amino acid sequence of approximately one-third of this protein and show that it has extensive homology with a newly defined family of Ca2+-binding proteins termed annexins. The partial sequence of the placental protein could be aligned with the sequence of either lipocortin I or calpactin I such that 49% and 58%, respectively, of the residues were identical. A comparison of the partial sequences of the placental protein with the partial sequence of bovine endonexin revealed 74% sequence identity. Based on this close relationship, the placental protein was named endonexin II. Equilibrium dialysis showed that endonexin II bound Ca2+ (Kd greater than 0.5 mM) and the affinity was increased by phosphatidylserine liposomes (kd approximately equal to 100 microM). In addition, endonexin II bound to phosphatidylserine- and phosphatidylethanolamine-containing liposomes in a Ca2+-dependent manner, and the binding was cooperative with respect to Ca2+ concentration (Hill constant greater than 3). The Ca2+- and phospholipid-binding properties of endonexin II raise the possibility that each of the four internally repeated sequences that have been demonstrated within this family of proteins contains a Ca2+-binding site.