Adsorption of pulmonary surfactant protein SP-A to monolayers of phospholipids containing hydrophobic surfactant protein SP-B or SP-C: potential differential role for tertiary interaction of lipids, hydrophobic proteins, and SP-A.

摘要

Surface balance techniques were used to study the interactions of surfactant protein SP-A with monolayers of surfactant components preformed at the air-water interface. SP-A adsorption into the monolayers was followed by monitoring the increase in the surface pressure Deltapi after injection of SP-A beneath the films. Monolayers of dipalmitoylphosphatidylcholine (DPPC):egg phosphatidylglycerol (PG) (8:2, mol/mol) spread at initial surface pressure pi(i) = 5 mN/m did not promote the adsorption of SP-A at a subphase concentration of 0.68 microg/mL as compared to its adsorption to the monolayer-free surface. Surfactant proteins, SP-B or SP-C, when present in the films of DPPC:PG spread at pi(i) = 5 mN/m, enhanced the incorporation of SP-A in the monolayers to a similar extent; the Deltapi values being dependent on the levels of SP-B or SP-C, 3-17 wt %, in the lipid films. Calcium in the subphase did not affect the intrinsic surface activity of SP-A but reduced the Deltapi values produced by the adsorption of the protein to all the preformed films independently of their compositions and charges. The divalent ions likely modified the interaction of SP-A with the monolayers through their effects on the conformation, self-association, and charge state of SP-A. Values of Deltapi produced by adsorption of SP-A to the films of DPPC:PG with or without SP-B or SP-C were a function of the initial surface pressure of the films, pi(i). In the range of pressures 5