What specific contribution do the 4 backbone carbonyls and Thr's OH have in the K+ channel?

The specific contribution of the four backbone carbonyls and the hydroxyl group of threonine (Thr) in the K+ channel is that they are involved in binding K+ ions by replacing water molecules. This is crucial for the functioning of the potassium channel, which facilitates the selective passage of potassium ions while preventing the passage of sodium ions and other smaller ions.

In the potassium channel, when K+ ions enter the pore, the surrounding water molecules are stripped away, a process that makes it possible for the ions to fit through the channel. The carbonyl oxygens from the backbone of the channel structure provide specific interactions with the K+ ion, stabilizing it in a dehydrated state. This interaction is essential for maintaining the selectivity and function of the channel, as the arrangement and electron density of the carbonyls are specifically tuned to accommodate K+ ions without allowing other ions to pass through effectively.

This highlights the importance of the channel's structural features in ion selectivity and conductivity, focusing on how the defined interactions with certain amino acid side groups and backbone elements enable the channel to perform its role effectively.