INTERACTIONS OF BENZODIAZEPINE DERIVATIVES WITH ANNEXINS

Human annexins III and V, members of the annexin family of calcium-and membrane-binding proteins, were complexed within the crystals with BD A452, a new 1,4-benzodiazepine derivative by soaking and co-crystalliz ation methods, The crystal structures of the complexes were analyzed b y x-ray crystallography and refined to 2.3- and 3.0-Angstrom resolutio n, BDA452 binds to a cleft which is located close to the N-terminus op posite to the membrane binding side of the proteins. Biophysical studi es of the interactions of various benzodiazepine derivatives with anne xins were performed to analyze the binding of benzodiazepines to annex ins and their effects on the annexin-induced calcium influx into phosp hatidylserine/phosphatidylethanolamine liposomes, Different effects we re observed with a variety of benzodiazepines and different annexins d epending on both the ligand and the protein, Almost opposite effects o n annexin function are elicited by BDA250 and diazepam, its 7-chloro-d erivative. We conclude that benzodiazepines modulate the calcium influ x activity of annexins allosterically by stabilizing or destabilizing the conducting state of peripherally bound annexins in agreement with suggestions by Kaneko.