Secondary structure in lung surfactant SP-B peptides: IR and CD studies ofbulk and monolayer phases

Pulmonary surfactant protein SP-B is known to facilitate adsorption and spr eading of surfactant components across the air/water interface. This proper ty appears essential for in vivo function in the alveolar subphase and at t he air/alveolar surface. Three peptides with amino acid sequences based on SP-B containing predicted alpha -helical regions (SP-B1-20, SP-B9-36A, SP-B 40-60A) have been synthesized to probe structure-function relationships and protein-lipid interaction in bulk phase and monolayer environments. IR and CD studies are reported along with traditional surface pressure-molecular area (pi -A) isotherms and IR reflection-absorption spectroscopy (IRRAS) in vestigations conducted at the air/water interface. In bulk phase, helix-pro moting environments (methanol and aqueous dispersions of lipid vesicles), S P-B1-20 and SP-B9-36A contained significant amounts of alpha -helical struc ture, whereas varying degrees of a-helix, random coil, and beta -sheet were observed in aqueous solutions and monolayers. The most striking behavior w as observed for SP-B9-36A, which displayed reversible surface pressure-indu ced beta -sheet formation. Bulk phase lipid melting curves and monolayer ex periments with peptide-lipid mixtures showed subtle differences in the degr ee of bulk phase interaction and substantial differences in peptide surface activity. The uniqueness of IRRAS is emphasized as the importance of evalu ating secondary structure in both bulk phase and monolayer environments for lung surfactant peptide mimics is demonstrated. (C) 2001 Elsevier Science B.V. All rights reserved.