Calbindin D28k exhibits properties characteristic of a Ca2+ sensor

J Biol Chem. 2002 May 10;277(19):16662-72. doi: 10.1074/jbc.M200415200. Epub 2002 Feb 28.


Calbindin D(28k) is a member of the calmodulin superfamily of Ca(2+)-binding proteins and contains six EF-hands. The protein is generally believed to function as a Ca(2+) buffer, but the studies presented in this work indicate that it may also act as a Ca(2+) sensor. The results show that Mg(2+) binds to the same sites as Ca(2+) with an association constant of approximately 1.4.10(3) m(-1) in 0.15 m KCl. The four high affinity sites in calbindin D(28k) bind Ca(2+) in a non-sequential, parallel manner. In the presence of physiological concentrations of Mg(2+), the Ca(2+) affinity is reduced by a factor of 2, 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 Ca(2+) concentration in a resting cell calbindin D(28k) is saturated to 40-75% with Mg(2+) but to less than 9% with Ca(2+). In contrast, the protein is expected to be nearly fully saturated with Ca(2+) at the Ca(2+) level of an activated cell. A substantial conformational change is observed upon Ca(2+) binding, but only minor structural changes take place upon Mg(2+) binding. This suggests that calbindin D(28k) undergoes Ca(2+)-induced structural changes upon Ca(2+) activation of a cell. Thus, calbindin D(28k) displays several properties that would be expected for a protein involved in Ca(2+)-induced signal transmission and hence may function not only as a Ca(2+) buffer but also as a Ca(2+) 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 Ca(2+), becomes exposed upon Ca(2+) binding.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Calbindin 1
  • Calbindins
  • Calcium / metabolism*
  • Cattle
  • Circular Dichroism
  • Humans
  • Magnesium / metabolism
  • Mass Spectrometry
  • Models, Statistical
  • Molecular Sequence Data
  • Protein Binding
  • Protein Conformation
  • Recombinant Proteins / metabolism
  • S100 Calcium Binding Protein G / chemistry*
  • Signal Transduction
  • Spectrometry, Fluorescence
  • Trypsin / pharmacology
  • Ultraviolet Rays


  • CALB1 protein, human
  • Calbindin 1
  • Calbindins
  • Recombinant Proteins
  • S100 Calcium Binding Protein G
  • Trypsin
  • Magnesium
  • Calcium