Calbindin D28k exhibits properties characteristic of a Ca2+ sensor.

Research output: Contribution to journalArticle

Abstract

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.

Details

Authors
Organisations
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Physical Chemistry

Keywords

  • 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
Original languageEnglish
Pages (from-to)16662-16672
JournalJournal of Biological Chemistry
Volume277
Issue number19
Publication statusPublished - 2002
Publication categoryResearch
Peer-reviewedYes

Bibliographic note

The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Biophysical Chemistry (LTH) (011001011), Connective Tissue Biology (013230151)