Multilayer formation upon compression of surfactant monolayers depends on protein concentration as well as lipid composition. An atomic force microscopy study.
The determinants for the formation of multilayers upon compression of surfactant monolayers were investigated by compressing films, beyond the squeeze-out plateau, to a surface tension of 22 millinewtons/m. Atomic force microscopy was used to visualize the topography of lipid films containing varying amounts of native surfactant protein B (SP-B). These films were compared with films containing synthetic peptides based on the N terminus of human SP-B: monomeric mSP-B-(1-25) or dimeric dSP-B-(1-25). The formation of typical hexagonal network structures as well as the height of protrusions were shown to depend on the concentration of SP-B. Protrusions of bilayer height were formed from physiologically relevant concentrations of 0.2-0.4 mol % (4.5-8.5 wt %) SP-B upwards. Much higher concentrations of SP-B-(1-25) peptides were needed to obtain network structures, and protrusion heights were not equal to those found for films with native SP-B. A striking observation was that while protrusions formed in films of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/1,2-dipalmitoyl-sn-glycero-3-(phospho-rac-(1-glycerol)) (DPPG) (80/20) had single bilayer thickness, those formed in DPPC/1-palmitoyl-2-oleoyl-sn-glycero-3-(phospho-rac-(1-glycerol)) (80/20) had various heights of multilayers, whereas those seen in DPPC/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine/DPPG (60/20/20) were mainly of bilayer height. For the first time direct observations by atomic force microscopy show (i) that a certain minimal concentration of SP-B is required for the formation of layered protrusions upon film compression, (ii) that protrusion height depends on whether the phospholipids contain an unsaturated fatty acyl chain, and (iii) that protrusion height also depends on whether the unsaturated acyl chain is present in phosphatidylcholine or in phosphatidylglycerol.
Diemel
Robert V
RV
Department of Biochemistry and Cell Biology, Graduate School of Animal Health, Faculty of Veterinary Medicine, Utrecht University, PO Box 80176, 3508 TD Utrecht, The Netherlands.
Snel
Margot M E
MM
Waring
Alan J
AJ
Walther
Frans J
FJ
van Golde
Lambert M G
LM
Putz
Günther
G
Haagsman
Henk P
HP
Batenburg
Joseph J
JJ
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D019281:Dimerization; D005227:Fatty Acids / Q000737:chemistry; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry*; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D010715:Phosphatidylglycerols / Q000737:chemistry; D011312:Pressure; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011510:Proteolipids / Q000378:metabolism; D011663:Pulmonary Surfactants / Q000378:metabolism; D013501:Surface-Active Agents / Q000378:metabolism*
D005227:Fatty Acids; D008051:Lipid Bilayers; D008055:Lipids; D010455:Peptides; D010715:Phosphatidylglycerols; D011510:Proteolipids; D011663:Pulmonary Surfactants; D013501:Surface-Active Agents; D015060:1,2-Dipalmitoylphosphatidylcholine; C030345:1,2-dipalmitoylphosphatidylglycerol