Sep 17, 2011

Lactadherin binds to phosphatidylserine-containing vesicles in a two-step mechanism sensitive to vesicle size and composition

Biochimica Et Biophysica Acta
Daniel OtzenJan T Rasmussen

Abstract

Lactadherin binds to phosphatidylserine (PS) in a stereospecific and calcium independent manner that is promoted by vesicle curvature. Because membrane binding of lactadherin is supported by a PS content of as little as 0.5%, lactadherin is a useful marker for cell stress where limited PS is exposed, as well as for apoptosis where PS freely traverses the plasma membrane. To gain further insight into the membrane-binding mechanism, we have utilized intrinsic lactadherin fluorescence. Our results indicate that intrinsic fluorescence increases and is blue-shifted upon membrane binding. Stopped-flow kinetic experiments confirm the specificity for PS and that the C2 domain contains a PS recognition motif. The stopped-flow kinetic data are consistent with a two-step binding mechanism, in which initial binding is followed by a slower step that involves either a conformational change or an altered degree of membrane insertion. Binding is detected at concentrations down to 0.03% PS and the capacity of binding reaches saturation around 1% PS (midpoint 0.15% PS). Higher concentrations of PS (and also to some extent PE) increase the association kinetics and the affinity. Increasing vesicle curvature promotes association. Remarkably, replac...Continue Reading

Mentioned in this Paper

Calcium [EPC]
Tissue Membrane
PAS-7 glycoprotein, Bos taurus
Unilamellar Vesicles
Calcium
Phosphatidylserines
Tertiary Protein Structure
Macromolecular Alteration
Phosphatidylethanolamine
Fluorescence Spectroscopy

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