Annexins V and XII insert into bilayers at mildly acidic pH and form ion channels.

Isas JM, Cartailler JP, Sokolov Y, Patel DR, Langen R, Luecke H, Hall JE, Haigler HT
Biochemistry. 2000 39 (11): 3015-22

PMID: 10715122 · DOI:10.1021/bi9922401

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.

MeSH Terms (19)

Alkanesulfonic Acids Animals Annexin A5 Annexins Azirines Buffers Humans Hydra Hydrogen-Ion Concentration Iodine Radioisotopes Ion Channels Lipid Bilayers Morpholines Phospholipids Photoaffinity Labels Polyethylene Glycols Sodium Acetate Spin Labels Tromethamine

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