Just a few changes in a specific ion channel in the body’s cells causes the whole body to shut down. Now, for the first time, researchers have mapped the structure of this sodium leak channel.
The cells of the human body function only because they are strictly regulated by numerous pumps and channels in the membranes.
These channels ensure that various molecules and ions can pass in and out of the cell so that the cell is in functional balance at all times. Some do this actively as pumps, and others just act as passive channels that enable substances to flow from inside the cells to the surroundings and vice versa.
One of these channels is the sodium leak channel, non-selective (NALCN), which ensures conductivity across the cell membrane and is especially relevant for background conductance in neurons.
Mutations in NALCN can cause severe nervous system disorders and early death, which doctors today cannot remedy. The efforts of future drug developers would therefore benefit from knowing the structure of NALCN and what goes wrong when it malfunctions.
Through collaborations, researchers from the University of Copenhagen have contributed to mapping this structure. The research has been published in Nature.
“There has long been great interest in mapping the structure of NALCN, but because of its nature, this was not possible until all the proteins that interact with NALCN to make it function were identified. We have succeeded in doing this,” explains Stephan Alexander Pless, Professor, Department of Drug Design and Pharmacology, University of Copenhagen.
Mutations in NALCN lead to rare diseases
One reason researchers previously had great difficulty in studying NALCN is that its normal function is essential for organisms to survive at all.
Mice, for example, cannot survive without NALCN, and silencing the gene for NALCN in these animals therefore results in very little to study, since they die immediately after birth. NALCN is necessary for many neurons to function, and these neurons are required for animals to move and breathe.
Very rarely, human children are born with microscopic mutations in NALCN that prevent them, like the animals, from moving and breathing normally. They also have reverse circadian rhythms, and they tend to die before adulthood.
“The problem with understanding these diseases has been that no one knew how NALCN works, in part because we could not map its structure. Treating people with the diseases and devising potential treatments has therefore not been possible,” explains Stephan Alexander Pless.
Four years to discover the relevant proteins
When researchers need to map the structure and function of a protein, they normally transfer the gene for the protein into a specialized cell line, induce the cells to express the protein and then study it using high-resolution microscopy.
However, this is easier said than done, because NALCN depends on other previously unknown proteins to function.
So when researchers transfer the gene for NALCN from an animal to an isolated cell, they end up with a non-functional protein that cannot be studied in any meaningful way.
The researchers in Stephan Alexander Pless laboratory have long studied NALCN, and they discovered that NALCN requires three other proteins to function.
Discovering the explanation and identifying the three proteins took 4 years, and this has finally enabled the genes for all the proteins to be transferred to a cell system, thereby enabling NALCN to be functionally expressed.
Collaborators in the United States then mapped the structure of the channel.
“Our part of the effort was to identify the proteins required for a functional NALCN, and collaborators mapped the structure of the proteins based on our earlier findings. As a result, we can finally present the structure of NALCN, which researchers have unsuccessfully tried to map for many years,” says Stephan Alexander Pless.
Mutations lead to more activity of NALCN
Once the researchers finally grasped the structure of NALCN, they could also investigate how mutations affect its function.
Today, about 100 people have mutations in NALCN or associated proteins, and by identifying the mutations and mapping on the structure of NALCN, the researchers found that most of the mutations were in the same region of the protein and that they actually enhanced NALCN’s function to a greater extent than nature intended.
“Disease often occurs when proteins malfunction, but here they actually work even better, and this can cause severe disorders. This affects the processes related to the neurons but also processes elsewhere in the body in which NALCN has an important function. This includes the pancreas, where NALCN likely plays a role for the insulin-producing beta cells,” explains Stephan Alexander Pless.
Greater insight into the basics of the nervous system
Stephan Alexander Pless says that a handful of diseases are associated with NALCN and that researchers have only examined one in greater detail so far.
The long-term purpose of the research is to better understand how these diseases function and whether drugs can be developed against them and to advance researchers’ knowledge of the nervous system in general.
“NALCN is essential to neuronal functioning, and now that we know how it works and looks, we can also better understand how the neurons and the entire nervous system function. The nervous system is important for the whole body to function, so this is a cornerstone in the body’s basic functioning,” says Stephan Alexander Pless.