Fourier-transform infrared spectroscopy studies of lipid/protein interaction in pulmonary surfactant.
The thermotropic behavior of intact bovine lung surfactant and its hydrophobic extract has been monitored via the temperature dependence of the 2850 cm-1 phospholipid acyl chain CH2 symmetric stretching frequencies in the IR spectrum. A broad, reversible, melting event was noted from about 15 to 40 degrees C in both the lipid extract and the native surfactant. Slight protein-induced disordering of the lipid acyl chains was evident. The melting event was confirmed by differential scanning calorimetry. The major surfactant protein, a 30-36-kDa class of glycoprotein (SP-A), has been isolated from bovine lung lavage and purified by affinity chromatography. SP-A was reconstituted into a binary lipid mixture of acyl chain perdeuterated dipalmitoylphosphatidylcholine/dipalmitoylphosphatidylglycerol (DPPC-d62/DPPG, 85:15 w/w), a ratio which approximates that in surfactant. Use of DPPC-d62 permitted the FT-IR determination of the effect of protein on the thermotropic behavior of individual phospholipids in the binary mixture. High levels of SP-A induced an ordering of the phospholipids, as shown by an increase in the transition temperature of DPPC-d62 compared to the lipid model. In contrast, a mixture of the other surfactant proteins induced a progressive disordering of the phospholipids and disruption of the cooperativity of the melting event. Transition widths of about 3 degrees, 9 degrees, and 27 degrees were noted for protein:lipid ratios of 0, 1:1, and 2:1 (w/w), respectively. Possible roles for the various proteins in surfactant function are discussed in light of these data.
Reilly
K E
KE
Department of Chemistry, Newark College of Arts and Sciences, Rutgers University, New Jersey 07102.
Mautone
A J
AJ
Mendelsohn
R
R
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000378:metabolism; D000818:Animals; D002152:Calorimetry, Differential Scanning; D002417:Cattle; D002846:Chromatography, Affinity; D004591:Electrophoresis, Polyacrylamide Gel; D005583:Fourier Analysis; D006023:Glycoproteins / Q000378:metabolism; D010713:Phosphatidylcholines / Q000378:metabolism; D010715:Phosphatidylglycerols / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D011510:Proteolipids / Q000378:metabolism*; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000378:metabolism*; D013057:Spectrum Analysis; D013696:Temperature
D006023:Glycoproteins; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; D010743:Phospholipids; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D015060:1,2-Dipalmitoylphosphatidylcholine; C030345:1,2-dipalmitoylphosphatidylglycerol