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Structural Topologies of Phosphorylated and Non-phosphorylated Oligomeric Phospholamban in Lipid Membranes by a Hybrid NMR Approach

Phospholamban (PLN) is a single-pass membrane protein that regulates Ca2+ transport into the cardiac sarcoplasmic reticulum (SR) by binding the SR Ca2+-ATPase (SERCA). Non-phosphorylated PLN decreases SERCA's apparent Ca2+ affinity, reducing uptake in the SR. Phosphorylation reverses the inhibition, augmenting the relaxation of the cardiac muscle. In lipid membranes and micelles, both phosphorylated and non-phosphorylated PLN assemble into pentamers, whose biological role is under debate. Using a hybrid NMR approach, including solution, oriented, and magic angle spinning techniques, we determined the structures and membrane topology of both phosphorylated and non-phosphorylated PLN pentamers. The pentamers adopt a pinwheel topology, with the transmembrane helices assembled in a left-handed coiled-coil quaternary structure. These transmembrane domains form a narrow pore of ∼2 Å widths and ∼25 Å lengths held together by a Leu/Ile zipper. The dimension of this central pore does not enable the passage of ions, such as Ca2+ or Cl, and remains invariant upon phosphorylation. Thus, oligomerization regulates SERCA by tuning the concentration of PLN available to SERCA, thereby keeping the ATPase within a physiological window of inhibition. This integrative NMR approach is applicable to other membrane proteins, where multiple structural biology and biophysical approaches are necessary to elucidate their biological function.

Print publication date: 06 Mar 2014
Copyright year: 2014
Print ISBN: 978-1-84973-910-8
PDF eISBN: 978-1-78262-744-9
ePub eISBN: 978-1-78262-119-5
From the book series:
New Developments in NMR