Neutralization of the positive charges of surfactant protein C. Effects on structure and function.
Pulmonary surfactant protein C (SP-C) is a small, extremely hydrophobic peptide with a highly conservative primary structure. The protein is characterized by two adjacent palmitoylated cysteine residues, two positively charged residues (one arginine residue and one lysine residue) in the N-terminal region, and a long hydrophobic stretch. SP-C enhances the adsorption of phospholipids into an air-water interface. To determine the importance of the positively charged residues, we carried out experiments with natural porcine SP-C and modified porcine SP-C (SP-Cm) in which the positive charges had been blocked by phenylglyoxal. Circular dichroism experiments showed that SP-Cm had an increased content of alpha-helix. Natural SP-C, but not SP-Cm, catalyzed insertion of phospholipids into a monolayer at the airwater interface. This reduced insertion was due to a strong reduction of binding of phospholipid vesicles to the monolayer. The insertion catalyzed by the natural porcine SP-C was decreased by an increased pH of the subphase. In contrast to natural SP-C, SP-Cm induced lipid mixing between phospholipid vesicles. The extent of lipid mixing was a function of the SP-C content. We conclude that the positively charged residues of SP-C are important for the binding of phospholipid vesicles to the monolayer, a process that precedes the insertion of phospholipids into the monolayer.
Creuwels
L A
LA
Laboratory of Veterinary Biochemistry, Utrecht University, The Netherlands.
Boer
E H
EH
Demel
R A
RA
van Golde
L M
LM
Haagsman
H P
HP
D000818:Animals; D001120:Arginine / Q000737:chemistry / Q000187:drug effects; D002412:Cations / Q000737:chemistry; D002942:Circular Dichroism; D004560:Electricity; D008567:Membranes, Artificial; D010658:Phenylglyoxal / Q000494:pharmacology; D010743:Phospholipids / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011510:Proteolipids / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D011663:Pulmonary Surfactants / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D013329:Structure-Activity Relationship; D013500:Surface Tension; D013552:Swine; D017186:Titrimetry
D002412:Cations; D008567:Membranes, Artificial; D010743:Phospholipids; D011510:Proteolipids; D011663:Pulmonary Surfactants; D001120:Arginine; D010658:Phenylglyoxal