Biophysical Journal 56: 935-946 (1989)
© 1989 the Biophysical Society

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Van der Meer, B W Articles by Sims, P J Search for Related Content PubMed PubMed Citation Articles by Van der Meer, B W Articles by Sims, P J

Complement proteins C5b-9 induce transbilayer migration of membrane phospholipids.

Cardiovascular Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City 73104.

ABSTRACT

Transbilayer migration of membrane phospholipid arising from membrane insertion of the terminal human complement proteins has been investigated. Asymmetric vesicles containing pyrene-labeled phosphatidylcholine (pyrenePC) concentrated in the inner monolayer were prepared by outer monolayer exchange between pyrenePC-containing large unilamellar vesicles and excess (unlabeled) small unilamellar vesicles, using bovine liver phosphatidylcholine-specific exchange protein. After depletion of pyrenePC from the outer monolayer, the asymmetric large unilamellar vesicles were isolated by gel filtration and exposed to the purified C5b-9 proteins at 37 degrees C. Transbilayer exchange of phospholipid between inner and outer monolayers during C5b-9 assembly was monitored by changes in pyrene excimer and monomer fluorescence. Membrane deposition of the C5b67 complex (by incubation with C5b6 + C7) caused no change in pyrenePC fluorescence. Addition of C8 to the C5b67 vesicles resulted in a dose-dependent decrease in the excimer/monomer ratio. This change was observed both in the presence and absence of complement C9. No change in fluorescence was observed for control vesicles exposed to C8 (in the absence of membrane C5b67), or upon C5b-9 addition to vesicles containing pyrenePC symmetrically distributed between inner and outer monolayers. These data suggest that a transbilayer exchange of phospholipid between inner and outer monolayers is initiated upon C8 binding to C5b67. The fluorescence data were analyzed according to a "random walk" model for excimer formation developed for the case where pyrenePC is asymmetrically distributed between lipid bilayers. Based on this analysis, we estimate that a net transbilayer migration of approximately 1% of total membrane phospholipid is initiated upon C8 binding to C5b67. The potential significance of this transbilayer exchange of membrane phospholipid to the biological activity of the terminal complement proteins is considered.

This article has been cited by other articles:

				R. F.A. Zwaal and A. J. Schroit Pathophysiologic Implications of Membrane Phospholipid Asymmetry in Blood Cells Blood, February 15, 1997; 89(4): 1121 - 1132. [Full Text] [PDF]

				V. J. Christiansen, P. J. Sims, and K. K. Hamilton Complement C5b-9 Increases Plasminogen Binding and Activation on Human Endothelial Cells Arterioscler. Thromb. Vasc. Biol., January 1, 1997; 17(1): 164 - 171. [Abstract] [Full Text]