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Elsevier, Biophysical Chemistry, 3(113), p. 223-232, 2005

DOI: 10.1016/j.bpc.2004.09.008

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Structure and properties of phospholipid–peptide monolayers containing monomeric SP-B1–25

This paper was not found in any repository, but could be made available legally by the author.
This paper was not found in any repository, but could be made available legally by the author.

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Abstract

Epifluorescence microscopy was used to study the structure and phase behavior of phospholipid films containing a human-sequence monomeric SP-B(1-25) synthetic peptide (mSP-B(1-25)). Measurements were done directly at the air-water (A/W) interface on films in a Langmuir-Whilhelmy balance coupled to a fluorescence microscope and real-time detection system to yield an approximate optical resolution of 1 mum. Fluorescence was achieved by laser excitation of 2-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-dodecanoyl)-1-hexadecanoyl-sn-glycero-3-PC (BODIPY-PC, concentration </=1 mol%). The presence of mSP-B(1-25) in films of 4:1 (mol/mol) 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/1,2-dioleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (sodium salt) (DOPG) had a substantial effect on lipid morphology and phase behavior that depended on both surface pressure and peptide concentration (10, 5, and 1 wt.%). The mSP-B(1-25) peptide tended to fluidize phospholipid monolayers based on expanded molecular areas and reduced collapse pressures. In addition, epifluorescence measurements revealed the formation of solid-phase domains apparent as three-armed counterclockwise spirals separated from regions of fluid liquid-expanded phase domains in compressed phospholipid-peptide films. The appearance of these separated solid-phase domains resembled pure L-DPPC rather than the ensemble-type solid domains found in films of DPPC/DOPG alone and were most apparent when 10 wt.% mSP-B(1-25) was present. In contrast, films containing lower, more physiological mSP-B(1-25) contents of 5 and 1 wt.% exhibited a prominent intermediate 'dendritic' phase that increased in extent as surface pressure was raised. This phase was characterized by branching structures that formed a lattice-like mesh network with fluorescence intensities between a dye-depleted solid domain and a dye-enriched liquid phase. These results indicate that mSP-B(1-25) at near-physiological levels produces morphological changes in phospholipid monolayers analogous to those observed for native SP-B(1-79).