Synthetic null-cysteine phospholamban analogue and the corresponding transmembrane domain inhibit the Ca-ATPase.
Chemical synthesis, functional reconstitution, and electron paramagnetic resonance (EPR) have been used to analyze the structure and function of phospholamban (PLB), a 52-residue integral membrane protein that regulates the calcium pump (Ca-ATPase) in cardiac sarcoplasmic reticulum (SR). PLB exists in equilibrium between monomeric and pentameric forms, as observed by SDS-PAGE, EPR, and fluorescence. It has been proposed that inhibition of the pump is due primarily to the monomeric form, with both pentameric stability and inhibition dependent primarily on the transmembrane (TM) domain. To test these hypotheses, we have studied the physical and functional properties of a synthetic null-cysteine PLB analogue that is entirely monomeric on SDS-PAGE, and compared it with the synthetic null-cysteine TM domain (residues 26-52). The TM domain was found to be primarily oligomeric on SDS-PAGE, and boundary lipid spin label analysis in lipid bilayers verified that the isolated TM domain is more oligomeric than the full-length parent molecule. These results indicate that the stability of the PLB pentamer is due primarily to attractive interactions between hydrophobic TM domains, overcoming the repulsive electrostatic interactions between the cationic cytoplasmic domains (residues 1-25). When reconstituted into liposomes containing the Ca-ATPase, the null-cysteine TM domain had the same inhibitory function as that of the full-length parent molecule. We conclude that the TM domain of PLB is sufficient for inhibitory function, the oligomeric stability of PLB does not determine its inhibitory activity, and the three Cys residues in the TM domain are not required for inhibitory function.
Karim
C B
CB
Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Marquardt
C G
CG
Stamm
J D
JD
Barany
G
G
Thomas
D D
DD
D000409:Alanine / Q000737:chemistry; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D002135:Calcium-Binding Proteins / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors* / Q000737:chemistry; D003545:Cysteine / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D008051:Lipid Bilayers / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry* / Q000494:pharmacology; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology; D010713:Phosphatidylcholines / Q000737:chemistry; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D000099211:Phospholamban
D000409:Alanine; D002135:Calcium-Binding Proteins; D000252:Calcium-Transporting ATPases; D003545:Cysteine; D004791:Enzyme Inhibitors; D008051:Lipid Bilayers; D008565:Membrane Proteins; D010446:Peptide Fragments; D010713:Phosphatidylcholines; D000099211:Phospholamban; C017251:1,2-oleoylphosphatidylcholine