Effects of KL4-Type Peptides on the Surface Activity and Stability of Pulmonary Surfactant Films as Evaluated in the Captive Bubble Surfactometer

Abstract

Although SP-B is the most critical protein in lung surfactant, recombinant or synthetic forms of SP-B as a basis for the development of therapeutic surfactants are still not available. An alternative is the design and production of peptides mimicking the structure and general properties of essential motifs in SP-B.In the present study the surface activity of different KL4-derived peptides, as sequence variations of the original peptide designed to replicate a general amphipathic motif of SP-B [1], has been assessed in the captive bubble surfactometer. The peptides were reconstituted in a surfactant lipid matrix: DPPC/POPC/POPG (50:25:15, w/w/w). This mixture was selected because it offers a fluid environment where the interfacial stability of surfactant films has to be provided primarily by the SP-B mimetic and not by the lipid moiety.Presence of just 1% (w/w) peptide KL4 (KLLLLKLLLLKLLLLKLLLLK) provided to the lipid mixture similar ability to adsorb at the interface than the presence of 1% native SP-B purified from porcine lungs. Films made of DPPC/POC/POPG/KL4 showed also similar ability to reach very low surface tension with limited compression than exhibited by films containing native SP-B, both under quasi-static and dynamic compression-expansion cycling. A KL4 peptide with amidated end showed similar surface activity, as well as a KL4 version including a PQ insertion in the middle of the sequence to break the alpha-helical conformation. In contrast, variants with reduced numbers of leucine residues showed significantly reduced ability to promote interfacial adsorption and much worse activity under compression-expansion cycling. These results support the concept that hydrophobicity and potential leucine-promoted peptide-peptide interactions are more important than helicity for SP-B-like surface activity.[1] Cochrane and Revak (1991), Science 254, 566-568