2. Lomize AL, Pogozheva ID, Mosberg HI. Anisotropic solvent model of the lipid bilayer. 2. Energetics of insertion of small molecules, peptides, and pro- teins in membranes. J Chem Inf Model 2011, 51:930-946. 3. Lomize AL, Reibarkh MY, Pogozheva ID. Interatomic potentials and solva- tion parameters from protein engineering data for buried residues. Protein Sci 2002, 11:1984-2000. 4. Lomize AL, Pogozheva ID, Mosberg HI. Quantification of helix-helix binding affinities in micelles and lipid bilayers. Protein Sci 2004, 13:2600- 2612 2501-Pos Board B271 Effects of KL4-Type Peptides on the Surface Activity and Stability of Pulmonary Surfactant Films as Evaluated in the Captive Bubble Surfactometer Olga Lucia Ospina Ramirez 1,2 , Jesus Perez-Gil 1 , Ismael Mingarro 3 . 1 Universidad Complutense de Madrid, Madrid, Spain, 2 Pontificia Universidad Javeriana, Bogota, Colombia, 3 Universidad de Valencia, Burjassot, Spain. 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 surfac- tants 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 am- phipathic motif of SP-B [1], has been assessed in the captive bubble surfactom- eter. 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 pro- vided 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 ad- sorption 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 sur- face activity. [1] Cochrane and Revak (1991), Science 254, 566-568 2502-Pos Board B272 Interaction of Hydrophobic Surfactant Proteins with Oriented Phospho- lipid Bilayers Kamlesh Kumar 1 , Ryan Loney 1 , Mariya Chavarha 1 , Shankar B. Rananavare 2 , Stephen B. Hall 1 . 1 Oregon Health & Sciences University, Portland, OR, USA, 2 Department of Chemistry, Portland State University, Portland, OR, USA. The hydrophobic surfactant proteins, SP-B and SP-C (SPs), promote rapid ad- sorption of phospholipids to an air-water interface by a mechanism that remains unclear. To understand the structural changes that lead to faster adsorption, we measured small-angle X-ray diffraction from dipalmitoylphosphatidylcholine (DPPC) bilayers containing varying concentration of SPs on solid supports. Swelling at different hydration allowed interpretation of the diffracted intensi- ties and construction of the electron density profile. With increasing concentra- tions of protein (0 - 10 wt/wt %), the d-spacing and bilayer thickness increased. This change may reflect stretching of the hydrophobic region of the bilayer caused by the presence of the protein. Larger amounts of protein also flattened the electron density profiles, reducing the difference between minimum and maxi- mum densities. A disordering effect of the proteins should cause greater thermal fluc- tuations of the bilayer, which would explain both the flattened density profile and the ob- served loss of higher order Bragg peaks. Acknowledgements: Stanford Synchrotron Radiation Lightsource (SSRL); NIH. 2503-Pos Board B273 Anionic Phospholipids change the Effect of the Hydrophobic Surfactant Proteins on Structures of Hexagonal Lipids Mariya Chavarha 1 , Ryan Loney 1 , Kamlesh Kumar 1 , Shankar B. Rananavare 2 , Stephen B. Hall 1 . 1 Oregon Health & Science University, Portland, OR, USA, 2 Portland State University, Portland, OR, USA. Available evidence suggests that the hydrophobic surfactant proteins (SPs), SP-B and SP-C, accelerate adsorption of surfactant vesicles to an air/water in- terface by promoting formation of a negatively curved rate-limiting structure. In support of this model, the proteins induce several phosphatidylethanol- amines to form inverse bicontinuous cubic phases, in which each leaflet has negative saddle-like curvature analogous to the hypothetical intermediate. The proteins could promote formation of cubic phases by changing spontane- ous curvature (c 0 ) of lipids, which would be reflected in the dimensions of the inverse hexagonal (H II ) phase. With 1,2-dioleoyl phosphatidylethanolamine (DOPE), the SPs had no effect on the size of the H II phase, suggesting a constant c 0 . The study, however, lacked anionic phospholipids, which constitute ~10% (mol:mol) of phospholipids in lung surfactant, and could engage in selective in- teractions with the cationic SPs. In this work, we used small-angle X-ray scat- tering to examine how SPs affect structures formed by DOPE mixed with 10% (mol:mol) anionic 1,2-dioleoyl phosphatidylglycerol (DOPG). With DOPG, the H II lattice-constant (a 0 ) decreased in a dose-dependent manner with increas- ing levels of protein. This change could be caused by specific interactions be- tween the SPs and DOPG, or nonspecific interactions between cationic SPs and the anionic phosphate group of DOPG. To determine whether the observed change in a 0 was caused by nonspecific electrostatic effects, the measurements were repeated on samples prepared in buffered electrolyte. In the presence of counterions, the effect of SPs on a 0 was significantly diminished. These results suggest that the change in the a 0 for DOPE:DOPG in the absence of counterions is caused by nonspecific electrostatic interactions between the positively- charged proteins and anionic phospholipids, and are unlikely to play a major role in physiological media. Acknowledgements: Stanford Synchrotron Radiation Lightsource; NIH. 2504-Pos Board B274 Effects of Hidrophobic Surfactant Proteins SP-B and SP-C on the Mechan- ical Properties and Structural Stability of Phospholipid Bilayers Elisa Parra, Lara H.-Moleiro, Ivan Lopez-Montero, Antonio Cruz, Francisco Monroy, Jesus Perez-Gil. Universidad Complutense De Madrid, Madrid, Spain. The respiratory surface is stabilized by pulmonary surfactant, a complex mix- ture of lipids and proteins, whose main function is reducing surface tension at the alveolar air-liquid interface in order to facilitate the work of breathing. It is composed by around 90% lipids and 8-10% specific proteins, including the hy- drophobic polypeptides SP-B and SP-C. A combined action of both proteins is essential for a proper organization of functional membrane arrays in surfactant complexes. SP-B and SP-C have dramatical effects on membrane structure and dynamics. In the present study we compare some structural, mechanical and dynamical properties of model POPC vesicles in the absence and presence of them, either in their physiological combined proportion or each protein by itself. Structural effects caused by hydrophobic surfactant proteins were noticed both by optical microscopy of giant proteolipid vesicles and by electron microscopy of 100 nm diameter extruded vesicles. Also, impermeable POPC membranes became per- meable when supplemented with any of these proteins. Significant differences were noticed between the effect of SP-B and SP-C on giant vesicles: suspen- sions containing only SP-B were stable but those containing only SP-C were quite dynamic, undergoing frequent fluctuations, reorganizations and ruptures as observed under the microscope. In order to investigate the physical explana- tion of these phenomena, mechanical studies have been carried out with giant phospholipid and proteolipid vesicles. The differences found between the effect of each protein separately and their physiological mixture support the concept that SP-B and SP-C mutually mod- ulate their membrane-perturbing properties, which may be crucial for the struc- ture, arrangement and dynamics of pulmonary surfactant membranes. 2505-Pos Board B275 Peptide-Lipid Reactivity in Membranes Robert H. Dods, Jackie A. Mosely, John M. Sanderson. Durham University, Durham, United Kingdom. Acyl transfer from lipids to peptides is able to occur in the absence of enzyme catalysis. This innate reactivity is of fundamental interest, with the potential to influence a number of membrane processes. The kinetics and selectivity of the Figure 1: Electron density profiles of DPPC samples containing vary- ing amount of SPs. Tuesday, February 28, 2012 491a