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Portrait of Sara Snogerup Linse

Sara Linse


Portrait of Sara Snogerup Linse

Calbindin D28k exhibits properties characteristic of a Ca2+ sensor.


  • Tord Berggård
  • Simona Miron
  • Patrik Önnerfjord
  • Eva Thulin
  • Karin S Akerfeldt
  • Jan J Enghild
  • Mikael Akke
  • Sara Linse

Summary, in English

Calbindin D28k is a member of the calmodulin super-family of Ca2+ -binding proteins and contains six EF-hands. The protein is generally believed to function as a Ca2+ buffer, but the studies presented in this work indicate that it may also act as a Ca2+ sensor. The results show that Mg2+ binds to the same sites as Ca2+ with an association constant of approximately 1.4 x 10(3) M-1 in 0.15 M KCl. The four high-affinity sites in calbindin D28k bind Ca2+ in a non-sequential, parallel manner. In the presence of physiological concentrations of Mg2+, the Ca2+ -affinity is reduced by a factor of two and the cooperativity, which otherwise is modest, increases. Based on the binding constants determined in the presence of physiological salt concentrations, we estimate that at the Ca2+ concentration in a resting cell calbindin D28k is saturated to 40-75% with Mg2+, but to less than 9 % with Ca2+. In contrast, the protein is expected to be nearly fully saturated with Ca2+ at the Ca2+ level of an activated cell. A substantial conformational change is observed upon Ca2+ binding, but only minor structural changes take place upon Mg2+-binding. This suggests that calbindin D28k undergoes Ca2+ -induced structural changes upon Ca2+ activation of a cell. Thus, calbindin D28k displays several properties that would be expected for a protein involved in Ca2+ -induced signal transmission and hence may function not only as a Ca2+ buffer, but also as a Ca2+ sensor. Digestion patterns resulting from limited proteolysis of the protein suggest that the loop of EF-hand 2, a variant site that does not bind Ca2+, becomes exposed upon Ca2+ binding.


  • Biophysical Chemistry
  • Rheumatology

Publishing year







Journal of Biological Chemistry





Document type

Journal article


American Society for Biochemistry and Molecular Biology


  • Physical Chemistry


  • Spectrum Analysis
  • Animal
  • Amino Acid Sequence
  • Calcium/*metabolism
  • Calcium-Binding Protein
  • Vitamin D-Dependent/*chemistry
  • Cattle
  • Circular Dichroism
  • Human
  • Magnesium/metabolism
  • Models
  • Statistical
  • Molecular Sequence Data
  • Protein Binding
  • Protein Conformation
  • Recombinant Proteins/metabolism
  • Signal Transduction
  • Fluorescence
  • Spectrometry
  • Mass
  • Support
  • Non-U.S. Gov't
  • U.S. Gov't
  • Non-P.H.S.
  • Trypsin/pharmacology
  • Ultraviolet Rays




  • ISSN: 1083-351X