SYNTHETIC PEPTIDE-CONTAINING SURFACTANTS - EVALUATION OF TRANSMEMBRANE VERSUS AMPHIPATHIC HELICES AND SURFACTANT PROTEIN-C POLY-VALYL TO POLY-LEUCYL SUBSTITUTION

Pulmonary surfactant contains two hydrophobic proteins, SP-B and SP-C. With the aim of identifying synthetic SP-B and SP-C substitutes for r eplacement therapy of respiratory distress syndromes, we have studied two transmembrane peptides and two amphipathic peptides that are locat ed in the plane of a phospholipid bilayer. One amphipathic peptide was designed by changing the amino acid sequence, but not the composition or size, of the 21-residue peptide KL4. This peptide, designated KL4. from its spacing of nonpolar and polar residues, exhibited similar al pha-helical content as KL4 but was oriented along a phospholipid bilay er plane, in contrast to the transmembrane orientation of KL4 in the s ame environment. The second amphipathic peptide analyzed was succinyl- LLEKLLEWLK-amide (WMAP10). KL4 more efficiently accelerated the spread ing of a mixture of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (Pam(2 )-GroPCho)/phosphatidylglycerol (PtdGro)/palmitic acid (PamOH), 68:22: 9 (by mass), at an air/water interface than did any of the amphipathic peptides. Similarly KL4, but not KL2,3, when present in an interfacia l monolayer composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglyce rol, 7:3 (by mass), increased lipid insertion from subphase vesicles. An SP-C analogue, SP-C(Leu), with all helical valyl residues in native SP-C replaced with Leu and the palmitoylcysteines at positions 5 and 6 replaced with Ser, but otherwise with essentially the same primary s tructure as the native peptide, was analyzed. SP-C(Leu) exhibited simi lar a-helical content as native SP-C and a transmembrane orientation a nd, in contrast to poly-valyl-containing synthetic peptides, it folds into a helical conformation after acid-induced denaturation. SP-C(Leu) accelerated the spreading of Pam(2)GroPCho/PtdGro/PamOH, 68:22:9 (by mass), almost identic ally to native SP-C, and lowered the surface ten sion during rapid cyclic film compressions in a pulsating bubble surfa ctometer to near zero and 43 mN/m at minimum and maximum bubble size, respectively, Airway instillation of 2% (by mass) SP-C(Leu) combined w ith Pam(2)GroPCho/PtdGro/PamOH in preterm rabbit fetuses improved dyna mic lung compliance by about 30% compared with untreated controls.