Annexin V perturbs or stabilises phospholipid membranes in a calcium-dependent manner.
The potency of annexin V to transport Ca2+ ions across phospholipid membranes was investigated, using large unilamellar phospholipid vesicles loaded with the Ca2+ indicator fura-2. It was demonstrated that annexin V leaves the vesicle membranes intact when added in the presence of 1 mM Ca2+. However, if the vesicles were first incubated with annexin V in the absence of Ca2+, subsequent addition of Ca2+ produced a fluorescence signal due to binding of Ca2+ to fura-2. Centrifugation of the vesicle suspension immediately thereafter showed that this signal originated from the supernatant and not from the sedimented vesicles. Our results show that annexin V causes loss of vesicle integrity in the absence of Ca2+, and leakage of trapped fura-2, rather than inward Ca2+ transport. Bovine serum albumin or Ca2+ concentrations higher than 2.5 mM also caused such fura-2 leakage. Apparently, calcium-dependent binding of annexin V to the membrane prevents aspecific membrane damage caused by this protein.
Goossens
E L
EL
Cardiovascular Research Institute Maastricht (CARIM), University of Limburg, Maastricht, The Netherlands.
Reutelingsperger
C P
CP
Jongsma
F H
FH
Kraayenhof
R
R
Hermens
W T
WT
D017304:Annexin A5 / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008563:Membrane Lipids / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*
D017304:Annexin A5; D015220:Calcium Channels; D008563:Membrane Lipids; D010743:Phospholipids; D002118:Calcium