Annexins V and XII insert into bilayers at mildly acidic pH and form ion channels.
The functional hallmark of annexins is the ability to bind to the surface of phospholipid membranes in a reversible, Ca(2+)-dependent manner. We now report that human annexin V and hydra annexin XII reversibly bound to phospholipid vesicles in the absence of Ca(2+) at low pH; half-maximal vesicle association occurred at pH 5.3 and 5. 8, respectively. The following biochemical data support the hypothesis that these annexins insert into bilayers at mildly acidic pH. First, a photoactivatable reagent (3-trifluoromethyl)-3-(m-[(125)I]iodophenyl)diazirine) which selectively labels proteins exposed to the hydrophobic domain of bilayers reacted with these annexins at pH 5.0 and below but not at neutral pH. Second, in a Triton X-114 partitioning assay, annexins V and XII act as integral membrane proteins at low pH and as hydrophilic proteins at neutral pH; in the presence of phospholipids half-maximal partitioning into detergent occurred at pH approximately 5.0. Finally, annexin V or XII formed single channels in phospholipid bilayers at low pH but not at neutral pH. A model is discussed in which the concentrations of H(+) and Ca(2+) regulate the reversible conversion of three forms of annexins-soluble, peripheral membrane, and transmembrane.
Isas
J M
JM
Department of Physiology and Biophysics, University of California, Irvine, California 92697, USA.
Cartailler
J P
JP
Sokolov
Y
Y
Patel
D R
DR
Langen
R
R
Luecke
H
H
Hall
J E
JE
Haigler
H T
HT
D017738:Alkanesulfonic Acids / Q000737:chemistry; D000818:Animals; D017304:Annexin A5 / Q000737:chemistry*; D017302:Annexins / Q000737:chemistry; D001389:Azirines / Q000737:chemistry; D002021:Buffers; D006801:Humans; D006829:Hydra; D006863:Hydrogen-Ion Concentration; D007457:Iodine Radioisotopes; D007473:Ion Channels / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D009025:Morpholines / Q000737:chemistry; D017830:Octoxynol; D010743:Phospholipids / Q000737:chemistry; D019920:Photoaffinity Labels / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D019346:Sodium Acetate / Q000737:chemistry; D013113:Spin Labels; D014325:Tromethamine / Q000737:chemistry
D017738:Alkanesulfonic Acids; D017304:Annexin A5; D017302:Annexins; D001389:Azirines; D002021:Buffers; D007457:Iodine Radioisotopes; D007473:Ion Channels; D008051:Lipid Bilayers; D009025:Morpholines; D010743:Phospholipids; D019920:Photoaffinity Labels; D013113:Spin Labels; D014325:Tromethamine; C004550:2-(N-morpholino)ethanesulfonic acid; D011092:Polyethylene Glycols; D019346:Sodium Acetate; C033174:3-(trifluoromethyl)-3-(3-iodophenyl)diazirine; D017830:Octoxynol; C010615:Nonidet P-40