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November 7, 2012--------News Archive Return to: News Alerts

The researchers’ starting point was the calcium pump located in the cell membrane of the model plant thale cress (Arabidopsis thaliana) (photo: Jørgen Nielsen)

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Ground-breaking Research About Cellular Calcium

When animals and plants are exposed to bacterial attack, odor and cold, calcium ions flow into the cells. Calcium signals cells with what is going on outside, but at high concentrations becomes toxic, so it must be quickly pumped out again – a feat accomplished very neatly by the cell's calcium pump

Researchers from the Danish National Research Foundation’s PUMPkin Centre at both the University of Copenhagen and Aarhus University have now shown that calcium pumps in the cell’s outer membrane adjust the pump speed very accurately to the internal calcium concentration.

Their findings have just been published in Nature.

“It turns out that the calcium pump can accurately
measure the cell’s calcium content and adjust its
speed in accordance with this information.

This prevents the concentration of calcium ions
in the cytoplasm from reaching a critical concentration
damaging the cells. The calcium pump is inactive when
concentration of calcium is low, but becomes activated
stepwise when the calcium concentration increases.”

Henning Tidow and Lisbeth Rosager Poulsen
Postdoctoral Fellows who took part in the joint research project

The researchers’ starting point was the calcium pump located in the cell membrane of the model plant thale cress (Arabidopsis thaliana), but the regulatory mechanism also applies to the corresponding calcium pump in humans and animals.

Calcium pumps bind two calmodulin proteins

Previous studies have shown that calcium pumps in both animals and plants work together with a protein called calmodulin. When there are many calcium ions in a cell, some of these bind to calmodulin, which is thereby able to activate the calcium pump.

“We purified the part of the calcium pump that interacts with calcium-activated calmodulin, and we managed to crystallise a protein complex. To our great surprise, we found that the calcium pump binds two calmodulin proteins, and not just one as always assumed,” explains Dr Tidow.

Calcium pump with three-step regulation

The fact that two calmodulin proteins are involved in the regulation of the calcium pump activity means that the calcium pump has three steps. It is switched off when no calcium-activated calmodulin is bound, it pumps at medium speed when binding occurs at one calmodulin protein, and it pumps at full speed when both calmodulin proteins are bound.

“Calcium pumps need considerable energy to transport calcium out of the cell. It is therefore important that they are only activated when there is a need to remove calcium. With two calmodulin-binding domains in the calcium pump, the cell can adjust the transportation to be energy efficient, at the same time as being able to quickly reduce the number of calcium ions if the concentration approaches a toxic level,” Dr Poulsen concludes.

Mathematics reveals biological function

Researchers also used mathematical network modelling
to further identify whether the calcium pump works
differently depending on whether it is activated by zero,
one or two calmodulin proteins – which revealed
another characteristic of calcium pump regulation
of calcium in the cell.

“We could see that the cell only responded to
incoming calcium when concentrations above
carefully defined threshold values were found.
This may be important for the way cells define
their status in the circadian rhythm or
during cell division, for example,”

Henning Tidow
Postdoctoral Fellow

The research – which may form the basis for the development of new drugs and new methods of food production – was carried out as a unique interdisciplinary collaboration between disciplines such as bioinformatics, protein crystallography, biophysics, enzyme kinetics, cell biology and particularly mathematical network modelling.

And also between researchers from Aarhus University and the University of Copenhagen at the Centre for Membrane Pumps in Cells and Disease (PUMPkin) – one of the Danish National Research Foundation’s Centres of Excellence – www.PUMPkin.au.dk

Basic research is important for applied research

The main objective of the research is how the control mechanisms of a biological pump works and which factors are involved in its' regulation. Results may form the foundation for breakthroughs in applied research.

The calcium pump and the sodium-potassium pump
are vital for the regulation of cardiac muscle activity,
and are targets for known drugs and the development
of new ones for improving treatment of cardiovascular
diseases. The blocking of ion pump activity is also an
obvious target for developing new drugs against
cancer and infectious diseases.

Calmodulin is a calcium-binding protein – a type of
calcium sensor – important to the regulation of
calcium by ion channel receptors.

The calcium-calmodulin complex activates a series
of enzymes within the cell, such as protein kinases,
which go on to regulate numerous other enzymes
and factors. So calmodulin mediates signalling
cascades within the cell – ‘it’s all about calcium.'

Calcium pumps are made up of protein molecules also known as Ca2+-ATPases. These pumps restore calcium balance in human cells following calcium-mediated signalling which comes from muscular effort, sensory input and nerve activity. Calcium pumps belong to a larger family of ion pumps called P-type ATPases, vital to life. The most well known is the sodium-potassium pump, discovered by Professor Jens Christian Skou of Aarhus University, who was awarded the Nobel Prize in Chemistry for his discovery in 1997.

A Long-standing collaboration

The scientists from Aarhus University and the University of Copenhagen are world renowned for their research into both crystal structures and the biochemical and biological characterisation of ion pumps.

This is not the first time the researchers from Aarhus and Copenhagen have published ground-breaking research results together in Nature. In 2007, the two research leaders Professor Poul Nissen and Professor Michael Broberg Palmgren published the world’s first structure of a biological pump from a plant. In close collaboration, they determined the structure of a proton pump from thale cress, and they explained how proton pumps can form the strong voltage across the plasma membrane that is a prerequisite for a plant’s uptake of nutrients from the soil.

Link to the research article in Nature:
A bimodular mechanism of calcium control in eukaryotes
Henning Tidow1,2*§, Lisbeth R. Poulsen1,3§, Antonina Andreeva4, Michael Knudsen1,5,
Kim L. Hein1,2#, Carsten Wiuf6, Michael G. Palmgren1,3 and Poul Nissen1,2*

1Centre for Membrane Pumps in Cells and Disease - PUMPKIN,
2Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10c, 8000 Aarhus C, Denmark
3Department of Plant Biology and Biotechnology, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark
4MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, UK
5Bioinformatics Research Centre, Aarhus University, C.F. Møllers Allé 8, 8000 Aarhus C,
6Department of Mathematical Sciences, University of Copenhagen, Universitetsparken 5, DK - 2100
Copenhagen, Denmark
*Corresponding authors: Henning Tidow, het@mb.au.dk and Poul Nissen, pn@mb.au.dk
#present address: Centre for Molecular Medicine Norway, Nordic EMBL Partnership, University of
Oslo, P.O. Box 1125, Blindern, N-0318 Oslo, Norway
§ H.T. and L.R.P. contributed equally

Postdoctoral Fellow Henning Tidow, +45 8942 5262, het@mb.au.dk
Professor Poul Nissen (Director of PUMPkin), +45 2899 2295, pn@mb.au.dk
Department of Molecular Biology and Genetics, PUMPkin
Aarhus University, Denmark

Postdoctoral Fellow Lisbeth Rosager Poulsen,, +45 3533 2595, lrpo@life.ku.dk
Professor Michael Broberg Palmgren, +45 3533 2592, palmgren@life.ku.dk
Department of Plant and Environmental Sciences, PUMPkin
University of Copenhagen, Denmark

Text: Inga Christensen Bach, Michael G. Palmgren (both the University of Copenhagen), Poul Nissen og Lisbeth Heilesen (both Aarhus University).

Original article: http://mbg.au.dk/en/news-and-events/news-item/artikel/danish-researchers-release-ground-breaking-knowledge-about-calcium-pumps-in-cells/