The structural properties of the transmembrane segment of the integral membrane protein phospholamban utilizing (13)C CPMAS, (2)H, and REDOR solid-state NMR spectroscopy.
Solid-state NMR spectroscopic techniques were used to investigate the secondary structure of the transmembrane peptide phospholamban (TM-PLB), a sarcoplasmic Ca(2+) regulator. (13)C cross-polarization magic angle spinning spectra of (13)C carbonyl-labeled Leu39 of TM-PLB exhibited two peaks in a pure 1-palmitoyl-2-oleoyl-phosphocholine (POPC) bilayer, each due to a different structural conformation of phospholamban as characterized by the corresponding (13)C chemical shift. The addition of a negatively charged phospholipid (1-palmitoyl-2-oleoylphosphatidylglycerol (POPG)) to the POPC bilayer stabilized TM-PLB to an alpha-helical conformation as monitored by an enhancement of the alpha-helical carbonyl (13)C resonance in the corresponding NMR spectrum. (13)C-(15)N REDOR solid-state NMR spectroscopic experiments revealed the distance between the (13)C carbonyl carbon of Leu39 and the (15)N amide nitrogen of Leu42 to be 4.2+/-0.2A indicating an alpha-helical conformation of TM-PLB with a slight deviation from an ideal 3.6 amino acid per turn helix. Finally, the quadrupolar splittings of three (2)H labeled leucines (Leu28, Leu39, and Leu51) incorporated in mechanically aligned DOPE/DOPC bilayers yielded an 11 degrees +/-5 degrees tilt of TM-PLB with respect to the bilayer normal. In addition to elucidating valuable TM-PLB secondary structure information, the solid-state NMR spectroscopic data indicates that the type of phospholipids and the water content play a crucial role in the secondary structure and folding of TM-PLB in a phospholipid bilayer.
Karp
Ethan S
ES
Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA.
Tiburu
Elvis K
EK
Abu-Baker
Shadi
S
Lorigan
Gary A
GA
D002135:Calcium-Binding Proteins / Q000737:chemistry*; D008051:Lipid Bilayers; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D010713:Phosphatidylcholines / Q000737:chemistry; D010715:Phosphatidylglycerols / Q000737:chemistry; D011487:Protein Conformation; D000099211:Phospholamban
D002135:Calcium-Binding Proteins; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; D000099211:Phospholamban; C060037:1-palmitoyl-2-oleoylglycero-3-phosphoglycerol; C028694:1-palmitoyl-2-oleoylphosphatidylcholine