European Biophysics Journal

, Volume 36, Issue 4, pp 415–424

Annexin A4 binding to anionic phospholipid vesicles modulated by pH and calcium

Article

DOI: 10.1007/s00249-007-0147-1

Cite this article as:
Zschörnig, O., Opitz, F. & Müller, M. Eur Biophys J (2007) 36: 415. doi:10.1007/s00249-007-0147-1
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Abstract

Annexin A4 belongs to a class of Ca2+-binding proteins for which different functions in the cell have proposed, e.g. involvement in exocytosis and in the coagulation process. All these functions are related to the ability of the annexins to bind to acidic phospholipids. In this study the interaction of annexin A4 with large unilamellar vesicles (LUV) prepared from phosphatidylserine (PS) or from phosphatidic acid (PA) is investigated at neutral and acidic pH. Annexin A4 strongly binds to either lipid at acidic pH, whereas at neutral pH only weak binding to PA and no binding to PS occurs. Addition of 40 μM Ca2+ leads to a strong binding to the lipids also at neutral pH. This is caused by the different electric charge of the protein below and above its isoelectric point. Binding of annexin A4 induces dehydration of the vesicle surface. The strength of the effects is much greater at pH 4 than at pH 7.4. At pH 7.4 annexin A4 reduces the Ca2+-threshold concentration necessary to induce fusion of PA LUV. The Ca2+ induced fusion of PS LUV is not affected by annexin A4 at pH 7.4. At pH 4 annexin A4 induces fusion of either vesicles without Ca2+. Despite the low binding extents at neutral pH annexin A4 induces a Ca2+ independent leakage of PS- or PA-LUV. The leakage extent is increased at acidic pH. From the data two suggestions are made: (1) At pH 4 annexin A4 (at least partially) penetrates into the bilayer in contrast to the preferred location at the vesicle surface at neutral pH. The conformation of annexin A4 seems to be different at the two conditions. (2) At neutral pH, Annexin A4 seems to be able to bind two PA vesicles simultaneously; however, only one PS vesicle at the same time. This behavior might be related to a recently described double Ca2+ binding site, which appears to be uniquely suited for PS.

Keywords

Annexins Binding Calcium Fusion Dielectric constant Liposome 

Abbreviations

DPE

N-(6-dimethylaminonaphthalene-2-sulfonyl)-phosphatidylethanolamine

FRET

Fluorescence resonance energy transfer

HEPES

N-(2-hydroxyethyl)piperazine-N′-(2-ethansulfonic acid)

LUV

Large unilamellar vesicles

MLV

Multilamellar vesicles

NBD-PE

1-4-nitrobenz-2-oxa-1,3-diazol-phosphatidylethanolamine

PA

Phosphatidic acid

PC

Phosphatidylcholine

PE

Phosphatidylethanolamine

PS

Phosphatidylserine

Pyr-PC

3-Palmitoyl-2-(1-pyrenedecanoyl)-l-α-phosphatidylcholine

Rh-PE

Lissamine rhodamine B sulfonyl-phosphatidylethanolamine

Trp

Tryptophan

TMR

Tetramethylrhodamine

ANTS

1-aminonaphthalene-3,6,8-trisulfonic acid

DPX

p-xylenebis(pyridiium bromide)

Copyright information

© EBSA 2007

Authors and Affiliations

  • Olaf Zschörnig
    • 1
  • Frank Opitz
    • 1
  • Matthias Müller
    • 1
  1. 1.Institute of Medical Physics and BiophysicsUniversity of LeipzigLeipzigGermany

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