X-ray structure of a water-soluble analog of the membrane protein phospholamban: sequence determinants defining the topology of tetrameric and pentameric coiled coils

J Mol Biol. 2005 May 6;348(3):777-87. doi: 10.1016/j.jmb.2005.02.040.


Phospholamban (PLB) is a pentameric transmembrane protein that regulates the Ca(2+)-dependent ATPase SERCA2a in sarcoplasmic reticulum membranes. We previously described the computational design of a water-soluble variant of phospholamban, WSPLB, which reproduced many of the structural and functional properties of the native membrane-soluble protein. While the full-length WSPLB forms a pentamer in solution, a truncated variant forms very stable tetramers. To obtain insight into the tetramer-pentamer cytoplasmic switch, we solved the crystal structure of the truncated construct, WSPLB 21-52. This peptide has a heptad sequence repeat with Leu residues at a- and Ile at d-positions from residues 31-52. The crystal structure revealed that WSPLB 21-52 adopted an antiparallel tetrameric coiled coil. This topology contrasts with the parallel topology of an analogue of the coiled-coil of GCN4 with the same Leu(a) Ile(d) repeat. Analysis of these structures revealed how the nature of the partially exposed residues at e- and g-positions influence the topology formed by the bundle. We also constructed a model for the pentameric form of PLB using the coiled-coil parameters derived from a single monomer in the tetrameric structure. This model suggests that both buried and interfacial hydrogen bonds are important for stabilizing the parallel pentamer.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Calcium-Binding Proteins / chemistry*
  • Calcium-Binding Proteins / genetics
  • Calcium-Binding Proteins / metabolism
  • Crystallography, X-Ray
  • Hydrogen Bonding
  • Membrane Proteins / chemistry*
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Models, Molecular
  • Molecular Sequence Data
  • Peptides / chemistry
  • Peptides / genetics
  • Protein Conformation*
  • Water / chemistry*


  • Calcium-Binding Proteins
  • Membrane Proteins
  • Peptides
  • phospholamban
  • Water