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Calbindin D28k exhibits properties characteristic of a Ca2+ sensor.

Berggård, Tord LU ; Miron, Simona; Önnerfjord, Patrik LU ; Thulin, Eva LU ; Akerfeldt, Karin S; Enghild, Jan J; Akke, Mikael LU and Linse, Sara LU (2002) In Journal of Biological Chemistry 277(19). p.16662-16672
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... (More)
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. (Less)
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organization
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Contribution to journal
publication status
published
subject
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
in
Journal of Biological Chemistry
volume
277
issue
19
pages
16662 - 16672
publisher
ASBMB
external identifiers
  • wos:000175564500044
  • scopus:0037052337
ISSN
1083-351X
DOI
10.1074/jbc.M200415200
language
English
LU publication?
yes
id
07c90401-d392-4790-b016-b987722dd88e (old id 106581)
date added to LUP
2007-06-29 08:53:20
date last changed
2017-08-20 03:42:14
@article{07c90401-d392-4790-b016-b987722dd88e,
  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.},
  author       = {Berggård, Tord and Miron, Simona and Önnerfjord, Patrik and Thulin, Eva and Akerfeldt, Karin S and Enghild, Jan J and Akke, Mikael and Linse, Sara},
  issn         = {1083-351X},
  keyword      = {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},
  language     = {eng},
  number       = {19},
  pages        = {16662--16672},
  publisher    = {ASBMB},
  series       = {Journal of Biological Chemistry},
  title        = {Calbindin D28k exhibits properties characteristic of a Ca2+ sensor.},
  url          = {http://dx.doi.org/10.1074/jbc.M200415200},
  volume       = {277},
  year         = {2002},
}