SP-A forms extensive lattice-like structures on DPPC/rough-lipopolysaccharide mixed monolayers
IGNACIO GARCIA-VERDUGO 1, OLGA CANADAS 1, SVETLA G TANEVA 2, KEVIN M.W. KEOUGH 3 and CRISTINA CASALS 1*
1 COMPLUTENSE UNIVERSITY OF MADRID
2 Department of Biochemistry and Discipline of Pediatrics, Memorial University of Newfoundland
3 Alberta Heritage Foundation for Medical Research
* To whom correspondence should be addressed. E-mail: ccasalsc{at}bio.ucm.es.
Submitted on March 28, 2007
Revised on April 30, 2007
Accepted on 23 July 2007
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Abstract |
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Due to the inhalation of airborne particles containing bacterial lipopolysaccharide (LPS), these molecules might incorporate into the DPPC-rich monolayer and interact with surfactant protein A (SP-A), the major surfactant protein component involved in host defense. In this study, epifluorescence microscopy combined with a surface balance was used to examine the interaction of SP-A with mixed monolayers of DPPC/rough LPS (Re-LPS). Binary monolayers of Re-LPS plus DPPC showed negative deviations from ideal behavior of the mean areas in the films consistent with partial miscibility and attractive interaction between the lipids. This interaction resulted in rearrangement and reduction of the size of DPPC-rich solid domains in DPPC/Re-LPS monolayers. The adsorption of SP-A to these monolayers caused expansion in the lipid molecular areas. SP-A interacted strongly with Re-LPS and promoted the formation of DPPC-rich solid domains. Fluorescently labeled TR-SP-A accumulated at the fluid-solid boundary regions and formed networks of interconnected filaments in the fluid phase of DPPC/Re-LPS monolayers in a Ca2+-independent manner. These lattice-like structures were also observed when TR-SP-A interacted with lipid A monolayers. These novel results deepen our understanding of the specific interaction of SP-A with the lipid A moiety of bacterial lipopolysaccharide.
Key Words:
DPPC, Lipid A, Surfactant protein A, epifluorescence microscopy, monolayers, rough-lipopolysaccharide
