Hydrogen Bond Network Of Potassium Channel

The potassium to sodium ratio in your diet is important because it helps to determine the potassium sodium ratio inside and outside of your cells' membranes. This ratio inside and outside the membranes creates an electric field. The electric field is critical to the cell performing its proper functions.

Maintaining the proper ratio is important so that your cells can function at their best. The electric field in a cell can change many times a second. These changes are how the cell drives all of your cell processes. It works very much like an electric motor, which has a rotor that rotates as the electric field changes.

But instead of turning a rotor, the changes in electric field drive cell processes by changing the shapes of proteins inside the cell. When the electric field changes, the local forces holding the protein in a particular shape change and the protein may change shape.

Hydrogen Bond Quadruple AngewChemIntEd 1998 v37 p75
Dots represent hydrogen bonds

 
The change in these proteins' shapes is determined by the strength of local bonds inside the protein. The protein is folded into multiple types of shapes depending upon these bonds inside the protein. The bonds can be several different types. The last few posts talked about salt bridges. Salt bridges are bonds that are composed of electrostatic bonds and hydrogen bonds.

But hydrogen bonds can affect protein shapes and cell processes completely on their own. Hydrogen bonds are abundant throughout a cell. They are composed of a single hydrogen atom that is in position between two other types of molecules. These other molecules have areas that are negatively charged. The positively charged hydrogen locates itself between the negative charges. Instead of being bond tightly like a covalent bond, the attraction is weaker and more easily broken.

When the electric field inside your cell changes, the strength of the bond between the hydrogen and the negatively charged areas changes. If the change in the electric field is enough, the shape of the protein determined by these hydrogen bonds will change.

Potassium Channels

Potassium channels are proteins that we have been discussing quite a bit in the last few posts. They allow potassium to move across the cell membranes, thus changing the electric field.

In recent posts we discussed a gate inside the cell that opens and closes the potassium channel. The gate depends upon changing the position of salt bridges to open and close the channel. The salt bridges shift from one position to another when the strength of the electric field changes.

Selectivity Filters

But there are other mechanisms besides gates that can open or close a potassium channel. One of the other mechanisms that can open or close a potassium channel is a change in its selectivity filter. A selectivity filter is located on one end of the channel. This filter keeps out other ions and allows only potassium to enter the channel.

This is not completely true because on rare occasions a smaller sodium will get through. The reason the smaller sodium ion does not get through all the time is because both sodium and potassium have water loosely attached to themselves.

The size of the chamber of the filter allows potassium and its attached water to just fit. The filter then strips the water off the potassium, so that only the potassium ion goes through.

The smaller sodium ion plus water is too far away from the part of the filter that strips the water when it enters the filter. So its water does not get stripped off. But the sodium ion plus water is larger than a naked potassium ion, and thus is too large to get through the pore in the channel.

The Function Of The Selectivity Filter

The present study (1) looked at what is important for proper function of the selectivity filter, so that potassium can get through when it is supposed to, and is blocked when it should be blocked. The structure of the selectivity filter is highly conserved among all the various types of potassium channels, which means its structure is very important for it to work properly.

The researchers asked, “What are the aspects of the filter's structure that allow it to function properly?” Different parts of its structure were changed experimentally to find out if the change made any difference in function. One part of the filter has no hydrogen bonds and another part is made of a hydrogen bond network. The researchers investigated how important the hydrogen bond network is for proper function of the potassium channel.

They changed the amino acids in the protein of the selectivity filter. Some of the amino acids that were changed did not affect the hydrogen bond network in the selectivity filter, and some did. The researchers then applied electric fields that were similar to those found when the cells change their electric field during normal conditions.

They found that the functional structure of the selectivity filter was determined by the hydrogen bond network. As long as the ability to form hydrogen bonds was undisturbed by the amino acid that was changed, the filter functioned normally. This occurred when there were mutations that affected parts of the filter that were uninvolved with the hydrogen bond network.

However, this finding changed when the mutation involved amino acids that were part of the hydrogen bond network. If hydrogen bonds were not able to interact normally, the filter functioned abnormally. As a result the opening and closing of the filter was severely affected. Instead of a steady activity, the channel had long periods of inactivity followed by bursts of activity. Some abnormal medical conditions are associated with this type of activity.

Keep Your Cells Healthy

Our cells have developed many mechanisms to help keep a proper balance of potassium and sodium. There is a great deal of redundancy so that when one portion goes bad, other areas can make up for it. However, interacting with all the cell processes is the electric field of the cell. When this field is not optimal, the cell does not function as it should. Getting a high potassium sodium ratio in your daily diet will help your cells to maintain this electric field, and will help your cells to function optimally.
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1. A multipoint hydrogen-bond network underlying KcsA C-type inactivation. Cordero-Morales JF1, Jogini V, Chakrapani S, Perozo E. Biophys J. 2011 May 18;100(10):2387-93. doi: 10.1016/j.bpj.2011.01.073.