Investigating the interaction of saposin C with POPS and POPC phospholipids: a solid-state NMR spectroscopic study.
The interaction of Saposin C (Sap C) with negatively charged phospholipids such as phosphatidylserine (PS) is essential for its biological function. In this study, Sap C (initially protonated in a weak acid) was inserted into multilamellar vesicles (MLVs) consisting of either 1-palmitoyl-2-oleoyl-sn-glycero-3-[phospho-L-serine] (negatively charged, POPS) or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (neutrally charged, POPC). The MLVs were then investigated using solid-state NMR spectroscopy under neutral pH (7.0) conditions. The (2)H and (31)P solid-state NMR spectroscopic data of Sap C-POPS and Sap C-POPC MLVs (prepared under the same conditions) were compared using the (2)H order parameter profiles of the POPC-d(31) or POPS-d(31) acyl chains as well as the (31)P chemical shift anisotropy width and (31)P T(1) relaxation times of the phospholipids headgroups. All those solid-state NMR spectroscopic approaches indicate that protonated Sap C disturbs the POPS bilayers and not the POPC lipid bilayers. These observations suggest for the first time that protonated Sap C inserts into PS bilayers and forms a stable complex with the lipids even after resuspension under neutral buffer conditions. Additionally, (31)P solid-state NMR spectroscopic studies of mechanically oriented phospholipids on glass plates were conducted and perturbation effect of Sap C on both POPS and POPC bilayers was compared. Unlike POPC bilayers, the data indicates that protonated Sap C (initially protonated in a weak acid) was unable to produce well-oriented POPS bilayers on glass plates at neutral pH. Conversely, unprotonated Sap C (initially dissolved in a neutral buffer) did not interact significantly with POPS phospholipids allowing them to produce well-oriented bilayers at neutral pH.
Abu-Baker
Shadi
S
Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio, USA.
Qi
Xiaoyang
X
Lorigan
Gary A
GA
D000595:Amino Acid Sequence; D002244:Carbon / Q000737:chemistry; D002384:Catalysis; D004926:Escherichia coli / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008051:Lipid Bilayers; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D010713:Phosphatidylcholines / Q000737:chemistry*; D010718:Phosphatidylserines / Q000737:chemistry*; D010743:Phospholipids / Q000737:chemistry; D011485:Protein Binding; D049231:Saposins / Q000737:chemistry* / Q000378:metabolism; D013696:Temperature
D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D010743:Phospholipids; D049231:Saposins; C050294:1-palmitoyl-2-oleoylglycero-3-phosphoserine; D002244:Carbon; C028694:1-palmitoyl-2-oleoylphosphatidylcholine
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