MthK K⁺ Channel: PDB 1LNQ

This structure of the bacterial MthK Ca⁺⁺-gated K⁺ channel from Methanothermobacter thermautotrophic was solved by Y. Jiang, A. Lee, J. Chen, M. Cadene, B. T. Chait & R. MacKinnon in 2002. 

Suggested display options:

Use the right mouse button to color chain and display as cartoon. 

Select hetero-ligand and display as spacefill with color CPK to visualize Ca⁺⁺ ions bound to the large regulatory "gating ring."

Note: It is assumed that the large gating ring would normally associate with only one channel, although there is a channel on each side of it in the crystal.

Identify and zoom in on the core channel structure. (You may find it helpful in centering the channel to hold down the control key and right drag.)

Compare this structure of the open MthK channel to the closed KcsA channel viewed in the other Chime exercise.
To zoom in, left drag while holding down the shift key.
To center the channel, right drag while holding down the control key.

Questions:
Is the selectivity filter in the same location in the two channels? You can see where it is in this channel by typing into the command line select 59-63, enter, and then display ball & stick with color CPK.
Are the rings of oxygen atoms that define K⁺ binding sites in the same location as in the KcsA channel?

In the command line type in select gly83, enter, and then change the display of this residue to note its position.
Question: Is this glycine residue appropriately located to serve as a hinge when the innermost helix of each copy of the protein bends during channel opening?

Three residues in each copy of the gating ring protein interact with Ca⁺⁺.
To visualize these, type in select 184, 210, 212, enter, change the display to ball and stick and color CPK. Zoom in for a closer look.
Questions: What residues are these? (Hint: try clicking on them.)
Which atoms interact with Ca⁺⁺?
Can you name another calcium binding protein with similar Ca⁺⁺ binding ligands.

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