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Biophys. J. BioFAST: First Published November 17, 2006. doi:10.1529/biophysj.105.078592
© 2006 by the Biophysical Society.

A more recent version of this article appeared on February 15, 2007.
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MEMBRANES

Coadsorption of Human Milk Lactoferrin into the DPPC Phospholipid Monolayer Spread at the Air/water Interface

Fausto Miano 1, Xiubo Zhao 2, Jian Ren Lu 2* and Jeff Penfold 3

1 S.I.F.I. S.p.A.
2 University of Manchester
3 CCLRC

* To whom correspondence should be addressed. E-mail: j.lu{at}manchester.ac.uk.

Submitted on March 8, 2006
Revised on June 29, 2006
Accepted on 10 October 2006


  Abstract
The coasorption of human milk lactoferrin into a spread monolayer of DPPC at the air/water interface has been studied by neutron reflection. The system is a good model of the preocular tear film outer interface and this was the motivation for the study. The association of the protein with the surface was indicated by an increase of the surface pressure exerted by DPPC monolayer. The extent of lactoferrin coadsorption was found to decrease with increasing surface pressure in the lipid monolayer, a trend consistent with the observation reported for other proteins such as lysozyme and {beta}-lactoglobulin. The neutron reflectivity measurements were subsequently carried out at three surface pressures of 8, 15 and 35 mN/m in order to examine the structure and composition of lactoferrin co-adsorbed at the interface. Whilst DPPC monolayer effectively prevented lactoferrin insertion at the high surface pressure, a measurable amount of lactoferrin was found at the air/water interface at the two lower surface pressures. At 15 mN/m it was difficult to identify the distribution of lactoferrin with respect to the DPPC monolayer, due to its relatively low adsorbed amount and much broader distribution. At the lowest surface pressure of 8 mN/m, the lactoferrin co-adsorption was found to increase with time over the first few hours. After some 5hr the distribution of the lactoferrin layer became similar, though quantitatively lower, to that adsorbed in the absence of the DPPC monolayer. It is characterised by a top dense sublayer of 15 Å with a bottom diffuse sublayer of 60 Å, indicating structural unfolding induced by surface adsorption under these conditions.

Key Words: DPPC, Lactoferrin, interfacial interaction, model membrane, neutron reflection, protein penetration






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Copyright © 2006 by the Biophysical Society.