Examples of ion binding and membrane proteins

Hi all
The above title is one section of a load of notes I've been told to make
The only sort of thing I can think is like Fe-S clusters and haem groups in like electron transport and stuff... and I guess that does include membranes... but I'm just a little confused as its not something we've covered in lectures

Any ideas? Cheers

Reply 1

Revenged

Bekaboo

I had a lecture all about this today...

There are two types of intrinsic membrane proteins

Inotropic and metabotropic

Inotropic membrane proteins include nicotonic acetylcholine receptor,

You probably remember from A-level binds, the acetylcholine (or nicotine ) binds to the receptor, causes pores in the membrane to open, Na+ ions enter, depolarisation in the post-synaptic membrane

So,

Inotropic receptore -> Open pores in membrane

The other type are metabotropic receptors.

All metabotropic receptors do is phosphorylation of proteins (in a very roundabout way that seems fascinating to only the hard core biochemist - but I give you what I understood from today)

2 types: tyrosine-kinase linked, G protein linked

Tyrosine-kinase linked -> the insulin receptor

Insulin (hormone) binds to receptor by the alpha strands of liver cells

Tyrosine kinase in the beta strand phosphorylates the beta strand

This causes phosphorylation of proteins in the cell... conformational change... and quite how this causes all the effects of insulin - I don't know...

G protein...

This is a protein that travels through the protein 8 membrane... There are two mechanisms that G proteins work as...

Number 1)

Hormone binds,

GDP is phosphorylated to GTP

Conformational change in the protein (alpha part with GTP splits from the beta and gamma)

This GTP-alpha causes an enzyme to be activated

Causing the formation AMP -> cAMP

This is a secondary messanger which causes a protein kinase to phosphorylate a protein (which is the important part)

Number 2)

This time two different intracellular messangers are produced...

Diacylglycerol (DAG) and IP3

I don't know the mechanism but you guessed it, it causes prosphorylation of a protein by a protein kinase...

You get the jist of it though...

Reply 2

Rach 2nd

Revenged

Number 2)

This time two different intracellular messangers are produced...

Diacylglycerol (DAG) and IP3

I don't know the mechanism but you guessed it, it causes prosphorylation of a protein by a protein kinase...

You get the jist of it though...

Here's an example mechanism:

The SH2 domain of phosphoinositide 3-kinase (PI-3K) binds the phosphotyrosine residue on IRS-1. The PI-3K phosphorylates the membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP2) to give phophatidylinositol 3,4,5-trisphosphate (PIP3). The PIP3 binds protein kinase B (PKB), which is phosphorylated and activated by PDK1. The active PKB then phosphorylates serine and threonine residues on target proteins e.g. glycogen synthase kinase 3 (GSK3).

Reply 3

Revenged

Rach 2nd

I won't pretend to understand any of that because I don't...

But what happens in the second mecahnism is that calcium ions are released from the internal stores by the secondary messangers DAG and IP3 and this causes the phosphorylation of proteins... conformational changes...

Reply 4

Comp_Genius

Rach 2nd

we had a lecture on this too, i thought you were a first year medic too. :p:

Reply 5

Cirsium

Hehe ah Revenged... always my saviour
Rep as soon as I've got any to give

Reply 6

Rach 2nd

darkenergy

we had a lecture on this too, i thought you were a first year medic too. :p:

No, a first-year biochemist :smile:

Reply 7

Tom H

If you're talking about signalling from cell surface proteins, you have 3 main methods:

Gated (eg. Ion Channels (voltage or ligand gated))
Enzyme Linked (Serine/Threonine/Tyrosine kinases)
G-Protein Couples (although it should be noted that while G-Proteins are associated with the membrane they are not integral membrane proteins).

However signalling is kinda off topic, I guess. The only ion binding proteins I can think of off-hand that aren't involved in respiration are proteins like Calmodulin and Tropinin, both Ca2+ binding proteins. Oh, and most osmolarity receptors bind ions. KpdD (I think it was D) binds Potassium ions I think (although it could just be a general osmolarity detector, unsure on that).

With regards membrane proteins there are so many different types. Transmembrane (single pass, 7 pass), ones that are only integral to the bottom layer of the membrane and ones that are only integral to the top (forget what they're called :colondollar:

) and anchored proteins (ie by a GPI anchor). Within transmembrane you can have porins, ion channels (gated, facilitated or active), receptors which can have varying responses (serine/threonine/tyrosine phosphorylation, GEF domain activation for G-Protein activation).

You can also have membrane proteins that specifically associate with lipid rafts, via having longer than normal hydrophobic regions.