ionotropic glutamate receptors?

[scm007]

Anybody think they can give me an explanation of the structure and function of the ionotropic glutamate receptors? I understand the basic principals of the flux in calcium ions, spurring a realease of glutamate, which interact with the receptor proteins. But where exactly do the ionotropic glutamate receptors stand in this, are they simply one type of receptor protein? And if so, does anybody know what the primary, secondary, tertiary, and quarternery structures of these proteins are, and how they affect this whole process?

 

A term that I have come across is ligand gated ion channels. What are these?

 

Thanks in advance, and possibly this thread should be under the neuroscience section in the Medical Science seeing as how this operates in the brain. I know that these questions may be pretty specific, but give a go at whatever you know.

 

Thanks--Stephen

[scm007]

I'm guessing that nobody wants to field this?

[blike]

A term that I have come across is ligand gated ion channels. What are these?

I'm not sure about the first part of your post, it's a little beyond what I've read so far. Ligand gated ion channels are transmembrane channels that allow ions to flow in or out depending on equillibrium. The channels are open and closed by the ligands, which change the conformation of the protein.

[blike]

I looked a little on google. It seems as if ionotropic glutamate receptors are ligand gated ion channels. When glutamate is released from neighboring cells, it binds to the receptor which opens the channel. Ions can then rush in or out of the cell which causes a depolarization. It looks like the channel is divided into five subunits.

 

Remember that primary structure is the linear amino acid sequence of the protein. Secondary structures would be B-pleated sheets or alpha helices, which form due to hydrogen bonding. Tertiary structure of the protein is a complete comformation of a subunit of the protein. All four weak interactions are involved with this folding: ionic, Van der Waals, hydrogen bonding, and hydrophobic interactions. Covalent bonds also help stabilized this structure. They form between the sulfur atoms in adjacent cysteine molecules. The tertiary structure is responsible for the protein subunits behavior. Quaternary structure is the whole protein, including all the subunits.

 

Here's a great link: http://www.bris.ac.uk/Depts/Synaptic/info/glutamate.html

[scm007]

So how do the ligands control ions passing across the membrane? Do they bind with them to create molecules to large to go through the channels?

[blike]

The binding of the ligand changes the conformation of the protein, which allows the passage of the molecule.

[scm007]

And how does it change the conformation of the protein? And how does changing the conformation allow the protein to pass across the membrane?

[blike]

And how does it change the conformation of the protein?

 

I'm not quite sure why you're studying very specific ion gated channels when you havn't quite got a grip on proteins yet. I'm not trying to be condescending, just wondering if you're teaching yourself or if you're enrolled in a course that's throwing this at you without prior knowledge of general protein biology.

 

Anyhow, remember that the tertiary and quaternary structure of a protein is dictated by the four weak interactions [ionic, Van der Waals, hydrogen bonds, hydrophobic interactions]. A ligand binds to the protein by weak interactions as well. Most proteins are very specific for their ligands. In other words, the shape of the protein in it's unbound state naturally allows for close contact with the ligand. When a ligand forms bonds with the protein, other bonds are disrupted all along the structure of the protein. This causes a rearrangement in shape.

 

And how does changing the conformation allow the protein to pass across the membrane?

 

You've misunderstood me somewhere along the line. The protein is a transmembrane protein. In other words, one end is on the inside of the cell, and the other end is on the outside. Think of it as a tunnel. When the protein is in it's natural conformation, the tunnel is closed (because of the shape). When the ligand binds, the channel opens up. In this case, ions flow through when the channel is open.

[scm007]

Yes I was teaching myself. I must have missed that somewhere. Thanks.

[blike]

You're quite welcome. Feel free to post if you come across any more questions.