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Portrait of Sara Snogerup Linse

Sara Linse


Portrait of Sara Snogerup Linse

Coupling of ligand binding and dimerization of helix-loop-helix peptides: Spectroscopic and sedimentation analyses of calbindin D-9k EF-hands


  • Karin Julenius
  • James Robblee
  • Eva Thulin
  • Bryan E Finn
  • Robert Fairman
  • Sara Linse

Summary, in English

Isolated Ca2+-binding EF-hand peptides have a tendency to dimerize. This study is an attempt to account for the coupled equilibria of Ca2+-binding and peptide association for two EF-hands with strikingly different loop sequence and net charge. We have studied each of the two separate EF-hand fragments from calbindin D-9k. A series of Ca2+-titrations at different peptide concentrations were monitored by CD and fluorescence spectroscopy. All data were fitted simultaneously to both a complete model of all possible equilibrium intermediates and a reduced model not including dimerization in the absence of Ca2+. Analytical ultracentrifugation shows that the peptides may occur as monomers or dimers depending on the solution conditions. Our results show strikingly different behavior for the two EF-hands. The fragment containing the N-terminal EF-hand shows a strong tendency to dimerize in the Ca2+-bound state. The average Ca2+-affinity is 3.5 orders of magnitude lower than for the intact protein. We observe a large apparent cooperativity of Ca2+ binding for the overall process from Ca2+-free monomer to fully loaded dimer, showing that a Ca2+-free EF-hand folds upon dimerization to a Ca2+-bound EF-hand, thereby presenting a preformed binding site to the second Ca2+-ion. The C-terminal EF-hand shows a much smaller tendency to dimerize, which may be related to its larger net negative charge. In spite of the differences in dimerization behavior, the Ca2+ affinities of both EF-hand fragments are similar and in the range IgK = 4.6-5.3.


  • Biophysical Chemistry

Publishing year












Document type

Journal article


John Wiley & Sons Inc.


  • Physical Chemistry


  • Molecular
  • Models
  • Biological
  • Ligands
  • EF Hand Motifs
  • Dimerization
  • Cyanogen Bromide : chemistry
  • Comparative Study
  • Circular Dichroism
  • Cattle
  • Vitamin D-Dependent : metabolism
  • Calcium-Binding Protein
  • Vitamin D-Dependent : chemistry
  • Calcium : metabolism
  • Binding Sites
  • Amino Acid Sequence
  • Animal
  • Molecular Sequence Data
  • Peptide Fragments : chemistry
  • Protein Binding
  • Sequence Alignment
  • Spectrometry
  • Fluorescence




  • ISSN: 0887-3585