Novel organization and properties of annexin 2-membrane complexes.
Annexin 2 belongs to the annexin family of proteins that bind to phospholipid membranes in a Ca(2+)-dependent manner. Here we show that, under mild acidic conditions, annexin 2 binds to and aggregates membranes containing anionic phospholipids, a fact that questions the mechanism of its interaction with membranes via Ca(2+) bridges only. The H(+) sensitivity of annexin 2-mediated aggregation is modulated by lipid composition (i.e. cholesterol content). Cryo-electron microscopy of aggregated liposomes revealed that both the monomeric and the tetrameric forms of the protein form bridges between the liposomes at acidic pH. Monomeric annexin 2 induced two different organizations of the membrane junctions. The first resembled that obtained at pH 7 in the presence of Ca(2+). For the tetramer, the arrangement was different. These bridges seemed more flexible than the Ca(2+)-mediated junctions allowing the invagination of membranes. Time-resolved fluorescence analysis at mild acidic pH and the measurement of Stokes radius revealed that the protein undergoes conformational changes similar to those induced by Ca(2+). Labeling with the lipophilic probe 3-(trifluoromethyl)-3-(m-[(125)I]iodophenyl)diazirine indicated that the protein has access to the hydrophobic part of the membrane at both acidic pH in the absence of Ca(2+) and at neutral pH in the presence of Ca(2+). Models for the membrane interactions of annexin 2 at neutral pH in the presence of Ca(2+) and at acidic pH are discussed.
Lambert
Olivier
O
Unité de Biologie Cellulaire et Moléculaire de la Sécrétion, CNRS UPR 1929, Institut de Biologie Physico-Chimique, 75005 Paris, France.
Cavusoglu
Nükhet
N
Gallay
Jacques
J
Vincent
Michel
M
Rigaud
Jean Louis
JL
Henry
Jean-Pierre
JP
Ayala-Sanmartin
Jesus
J
D017306:Annexin A2 / Q000737:chemistry / Q000378:metabolism*; D020285:Cryoelectron Microscopy; D006863:Hydrogen-Ion Concentration; D008563:Membrane Lipids / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D017306:Annexin A2; D008563:Membrane Lipids; D010743:Phospholipids