Residue specific partitioning of KL4 into phospholipid bilayers |
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Authors: | Austin L Turner Otonye Braide Frank D Mills Gail E Fanucci Joanna R Long |
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Institution: | 1. Department of Chemistry, University of Florida, Gainesville, FL 32611, USA;2. Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA |
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Abstract: | KL4, which has demonstrated success in the treatment of respiratory distress, is a synthetic helical, amphipathic peptide mimetic of lung surfactant protein B. The unusual periodicity of charged residues within KL4 and its relatively high hydrophobicity distinguish it from canonical amphipathic helical peptides. Here we utilized site specific spin labeling of both lipids and the peptide coupled with EPR spectroscopy to discern the effects of KL4 on lipid dynamics, the residue specific dynamics of hydrophobic regions within KL4, and the partitioning depths of specific KL4 residues into the DPPC/POPG and POPC/POPG lipid bilayers under physiologically relevant conditions. KL4 induces alterations in acyl chain dynamics in a lipid-dependent manner, with the peptide partitioning more deeply into DPPC-rich bilayers. Combined with an earlier NMR study of changes in lipid dynamics on addition of KL4 (V.C. Antharam et al., 2009), we are able to distinguish how KL4 affects both collective bilayer motions and intramolecular acyl chain dynamics in a lipid-dependent manner. EPR power saturation results for spin labeled lipids demonstrate that KL4 also alters the accessibility profiles of paramagnetic colliders in a lipid-dependent manner. Measurements of dynamics and depth parameters for individual spin-labeled residues within KL4 are consistent with a model where the peptide partitions deeply into the lipid bilayers but lies parallel to the bilayer interface in both lipid environments; the depth of partitioning is dependent on the degree of lipid acyl chain saturation within the bilayer. |
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Keywords: | PS pulmonary surfactant SP-B surfactant protein B MLV multilamellar vesicle ARDS acute respiratory distress syndrome POPC 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine POPG 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol DPPC 1 2-dipalmitoyl-sn-glycero-3-phosphocholine n-doxyl-PSPC 1-palmitoyl-2-stearoyl-(n-doxyl)-sn-glycero-3-phosphocholine P/L peptide/lipid molar ratio CD circular dichroism FTIR Fourier transform infrared spectroscopy SDSL site-directed spin label CW-EPR continuous wave electron paramagnetic resonance ΔHpp peak-to-peak linewidth of central resonance line Bis-Tris 2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)-1 3-propanediol NiAA nickel (II) acetylacetonate NiEDDA nickel (II) ethylenediamine-N N&prime -diacetic acid TEMPO-PC 1-palmitoyl-2-stearoyl-sn-glycero-3-phospho(tempo)choline IAP iodoacetamido-PROXYL spin label |
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