Mr. Morrow et al., PULMONARY SURFACTANT-ASSOCIATED PROTEIN SP-B HAS LITTLE EFFECT ON ACYL CHAINS IN DIPALMITOYLPHOSPHATIDYLCHOLINE DISPERSIONS, Biochemistry, 32(16), 1993, pp. 4397-4402
Synthetic human pulmonary surfactant-associated protein SP-B has been
interacted with chain-perdeuterated dipalmitoylphosphatidylcholine (DP
PC-d62) in aqueous dispersions, and the dispersions were investigated
by magnetic resonance spectroscopy. The protein caused only small pert
urbations of the deuterium magnetic resonance spectra in the gel and l
iquid-crystal states. In an amount of 11% by weight in DPPC, it produc
ed a small reduction in the magnitude of the first moments of the spec
tra in the gel and a small increase (approximately 5%) in their magnit
ude in the liquid crystal. In the liquid crystal the protein was obser
ved to cause a similar effect on all portions of the acyl chain, as ob
served by its proportional shifting of splittings obtained from ''dePa
ked'' spectra. Using data from circular dichroism spectra, the protein
was found to be about 45% alpha-helical in methanol and in DPPC dispe
rsions. Alpha-helical content was not significantly changed by the pre
sence of 2 mM calcium or by the packing state of the acyl chains. The
presence of the protein enhanced the adsorption rate of lipid into the
air-water interface when dispersions of lipids or lipid plus SP-B wer
e injected below the interface. The results could be consistent with t
he protein interacting with the lipid near the head groups or arrangin
g itself around the edges of bilayer discs, or a combination of the tw
o orientations.