External reflection absorption infrared spectroscopy study of lung surfactant proteins SP-B and SP-C in phospholipid monolayers at the air/water interface.
The interactions of the hydrophobic pulmonary surfactant proteins SP-B and SP-C with 1,2-dipalmitoylphosphatidylcholine in mixed, spread monolayer films have been studied in situ at the air/water interface with the technique of external reflection absorption infrared spectroscopy (IRRAS). SP-C has a mostly alpha-helical secondary structure both in the pure state and in the presence of lipids, whereas SP-B secondary structure is a mixture of alpha-helical and disordered forms. When films of SP-B/1,2-dipalmitoylphosphatidylcholine are compressed to surface pressures (pi) greater than approximately 40-43 mN/m, the protein is partially (15-35%) excluded from the surface, as measured by intensity ratios of the peptide bond amide l/lipid C==O stretching vibrations. The extent of exclusion increases as the protein/lipid ratio in the film increases. In contrast, SP-C either remains at the surface at high pressures or leaves accompanied by lipids. The amide l peak of SP-C becomes asymmetric as a result of the formation of intermolecular sheet structures (1615-1630 cm-1) suggestive of peptide aggregation. The power of the IRRAS experiment for determination of film composition and molecular structure, i.e., as a direct test of the squeeze-out hypothesis of pulmonary surfactant function, is evident from this work.
Pastrana-Rios
B
B
Department of Chemistry, Rutgers University, Newark College of Arts and Science, New Jersey 07102, USA.
Taneva
S
S
Keough
K M
KM
Mautone
A J
AJ
Mendelsohn
R
R
D015060:1,2-Dipalmitoylphosphatidylcholine; D000388:Air; D000818:Animals; D008081:Liposomes; D008168:Lung; D017433:Protein Structure, Secondary; D011510:Proteolipids / Q000737:chemistry* / Q000302:isolation & purification; D011663:Pulmonary Surfactants / Q000737:chemistry* / Q000302:isolation & purification; D013055:Spectrophotometry, Infrared / Q000379:methods; D013552:Swine; D014867:Water
D008081:Liposomes; D011510:Proteolipids; D011663:Pulmonary Surfactants; D014867:Water; D015060:1,2-Dipalmitoylphosphatidylcholine