Kinetics of phospholipid insertion into monolayers

Authors: Michaela Ross Silke Krol Andreas Janshoff HansJoachim Galla

Publish Date: 2014/02/08

Volume: 31, Issue: 1, Pages: 52-61

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Abstract

The lung surfactant proteins SPB and SPC are pivotal for fast and reversible lipid insertion at the air/liquid interface a prerequisite for functional lung activity We used a model system consisting of a preformed monolayer at the air/liquid interface supplemented with surfactant protein SPB or SPC and unilamellar vesicles injected into the subphase of a film balance The content of SPB or SPC was similar to that found in lung lavage In order to elucidate distinct steps of lipid insertion we measured the timedependent pressure increase as a function of the initial surface pressure the temperature and the phosphatidylglycerol content by means of surface tension measurements and scanning force microscopy SFM The results of the film balance study are indicative of a twostep mechanism in which initial adsorption of vesicles to the proteincontaining monolayer is followed by rupture and integration of lipid material Furthermore we found that vesicle adsorption on a preformed monolayer supplemented with SPB or SPC is strongly enhanced by negatively charged lipids as provided by DPPG and the presence of Ca2+ ions in the subphase Hence longrange electrostatic interactions are thought to play an important role in attracting vesicles to the surface being the initial step in replenishment of lipid material While insertion into the monolayer is independent of the type of protein SPB or SPC initial adsorption is faster in the presence of SPB than SPC We propose that the preferential interaction between SPB and negatively charged DPPG leads to accumulation of negative charges in particular regions causing strong adhesion between DPPGcontaining vesicles and the monolayer mediated by Ca2+ ions which eventually causes flattening and rupture of attached liposomes as observed by in situ SFM

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