Structure and properties of phospholipid-peptide monolayers containing monomeric SP-B(1-25) I. Phases and morphology by epifluorescence microscopy.
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).
Biswas
Nilanjana
N
Department of Chemistry, University of Georgia, Athens, GA 30602-2556, USA.
Shanmukh
Saratchandra
S
Waring
Alan J
AJ
Walther
Frans
F
Wang
Zhendong
Z
Chang
Y
Y
Notter
Robert H
RH
Dluhy
Richard A
RA
D000388:Air; D001896:Boron Compounds / Q000737:chemistry; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry*; D008168:Lung / Q000378:metabolism; D008567:Membranes, Artificial; D008856:Microscopy, Fluorescence; D008968:Molecular Conformation; D010455:Peptides / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry; D010715:Phosphatidylglycerols / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry*; D011663:Pulmonary Surfactants / Q000737:chemistry; D013500:Surface Tension; D013816:Thermodynamics; D014867:Water
C095489:4,4-difluoro-4-bora-3a,4a-diaza-s-indacene; D001896:Boron Compounds; D008051:Lipid Bilayers; D008567:Membranes, Artificial; D010455:Peptides; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; D010743:Phospholipids; D011663:Pulmonary Surfactants; D014867:Water