Publication Date:
2012-10-23
Description:
Calcium ions (Ca(2+)) have an important role as secondary messengers in numerous signal transduction processes, and cells invest much energy in controlling and maintaining a steep gradient between intracellular ( approximately 0.1-micromolar) and extracellular ( approximately 2-millimolar) Ca(2+) concentrations. Calmodulin-stimulated calcium pumps, which include the plasma-membrane Ca(2+)-ATPases (PMCAs), are key regulators of intracellular Ca(2+) in eukaryotes. They contain a unique amino- or carboxy-terminal regulatory domain responsible for autoinhibition, and binding of calcium-loaded calmodulin to this domain releases autoinhibition and activates the pump. However, the structural basis for the activation mechanism is unknown and a key remaining question is how calmodulin-mediated PMCA regulation can cover both basal Ca(2+) levels in the nanomolar range as well as micromolar-range Ca(2+) transients generated by cell stimulation. Here we present an integrated study combining the determination of the high-resolution crystal structure of a PMCA regulatory-domain/calmodulin complex with in vivo characterization and biochemical, biophysical and bioinformatics data that provide mechanistic insights into a two-step PMCA activation mechanism mediated by calcium-loaded calmodulin. The structure shows the entire PMCA regulatory domain and reveals an unexpected 2:1 stoichiometry with two calcium-loaded calmodulin molecules binding to different sites on a long helix. A multifaceted characterization of the role of both sites leads to a general structural model for calmodulin-mediated regulation of PMCAs that allows stringent, highly responsive control of intracellular calcium in eukaryotes, making it possible to maintain a stable, basal level at a threshold Ca(2+) concentration, where steep activation occurs.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Tidow, Henning -- Poulsen, Lisbeth R -- Andreeva, Antonina -- Knudsen, Michael -- Hein, Kim L -- Wiuf, Carsten -- Palmgren, Michael G -- Nissen, Poul -- MC_U105192716/Medical Research Council/United Kingdom -- England -- Nature. 2012 Nov 15;491(7424):468-72. doi: 10.1038/nature11539. Epub 2012 Oct 21.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Centre for Membrane Pumps in Cells and Disease - PUMPKIN, Aarhus University, Gustav Wieds Vej 10c, DK-8000 Aarhus C, Denmark.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23086147" target="_blank"〉PubMed〈/a〉
Keywords:
Amino Acid Sequence
;
Arabidopsis/chemistry/enzymology/*metabolism
;
Arabidopsis Proteins/*chemistry/genetics/*metabolism
;
Binding Sites
;
Calcium/*metabolism
;
Calcium-Transporting ATPases/*chemistry/genetics/*metabolism
;
Calmodulin/*chemistry/metabolism
;
Enzyme Activation
;
Eukaryota/*metabolism
;
Intracellular Space/chemistry/metabolism
;
Models, Molecular
;
Molecular Sequence Data
;
Protein Binding
;
Protein Structure, Tertiary
;
Sequence Alignment
Print ISSN:
0028-0836
Electronic ISSN:
1476-4687
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
,
Natural Sciences in General
,
Physics
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