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Revision as of 01:36, 26 March 2012

Insulin Receptor

The receptor should be loaded as the dimer, and color chain so we can see it's a dimer. Orient it so the membrane would be at the bottom and explain this. First scene can include the antibody fragments (FABs) but then you should hide them in all the rest of the scenes to make it easier to focus on an understand the receptor.

Introduction

Every jmol window should have a caption so we know what we are looking at (include the name of the molecule and pdb code) Replace "insert caption here' with 'your caption'. This didn't work for me when the jmol window was not part of this section. Since you can have captions in every section, you can all make cool scenes & captions for consideration for the Molecular Playground.

The insulin receptor is a tyrosine kinase, that is a type of ligand-activated receptor kinase. Insulin receptors are expressed at the cell surface as disulfide-linked homodimers composed of alpha/beta . The folded over conformation of the ectodomain places ligands in the correct relative positions for activity. The receptor mediates activity by the addition of phosphate to tyrosines on specific proteins in cell. Tell us what we are looking at: ectodomain only (why?) What are the other parts? Explain color schemes. Orient us: where is the membrane? Where does ligand bind? "The folded over.." sentence doesn't make sense to me -- maybe later.

Insulin receptors are found in many diverse organisms organisms, from cnidarians and insects to humans. In humans, correctly functioning insulin receptors are essential for maintaining glucose levels in the blood. The insulin receptor also has role in growth and development (through insulin growth factor II); studies have shown that signalling through IGF2 plays a role in the mediation embryonic growth. ^[1]

In everyday function, insulin receptor substrate 1 (IRS-1) binding leads to increase in the high-affinity glucose transporter (Glut4) molecules on the outer membrane of the cell in muscle and adipose tissue. Glut4 mediates the transport of glucose into the cell, so an increase in Glut4 leads to increased glucose uptake. Insulin has two different receptor-binding surfaces on opposite sides of the molecule, that interact with two different sites on the insulin receptor. The first binding insulin surface interacts with a site on the L1 module as well as a 12-amino-acid peptide from the insert in Fn2. The second binding site consists of resides on the C-terminal portion of L2 and in the Fn1 and Fn2 modules ^[2]. Binding sites are shown highlighted in both monomers of the biologically fuctional dimer. ^[3]

Maintaining appropriate blood glucose levels is essential for appropriate life-sustaining metabolic function, and insulin receptor malfunction is associated with several severe diseases. Insulin insensitivity, or decreased insulin receptor signalling, leads to diabetes mellitus type 2. Type 2 diabetes is also known as non-insulin-dependent or adult onset diabetes, and is believed to be caused by a combination of obesity and genetic predisposition. In type 2 diabetes, cells are unable to uptake glucose due to decreased insulin receptor signaling, which leads to hyperglycemia (increased circulating glucose). Type 2 diabetes can be managed with dietary and lifestyle modifications to aid in proper metabolism.

Mutations in both copies of the insulin receptor gene causes Donohue syndrome, which is also known as leprechaunism. Donohue syndrome is an autosomal recessive disorder that results in a totally non-functional insulin receptor. The disorder results in distorted facial features, severe growth retardation, and often death within a year.^[4] A less severe mutation of the same gene causes a much milder form of the disease in which there is some insulin resistance but normal growth and subcutaneous fat distribution.^[5]

Overall Structure

The ectodomain of the insulin receptor is a of 2 identical monomers. Each v-shaped is composed of 6 domains, three on each side of the V, shown in different colors. It would be great if you inserted a color code in the text, listing the 6 domains each in their colors. And the text below could then be more concise with one sentence per domain: the red Leucine-rich domain is... The red domain is the (L1). This domain is involved in substrate binding. Its main feature is a 6 parallel stranded beta sheet. The orange domain is the (CR). It is composed mostly of loops and turns. The domain shown in yellow is a second (L2). It contains a five parallel stranded beta sheet and several surface alpha helices.

The next three domains are Fibronectin Type III domains. This type of domain is named after the protein fibronectin, which contains 16 of these domains. , with one antiparallel and one mixed beta sheet, is shown in green. , shown in blue, contains an insert domain of 120 residues. is shown in purple and contains just four beta strands.

I like how you step through these. Tell us fibronectin domains are beta sandwiches so we can look for that. Could you make the FnIII-2 domain insert light blue (and color code the word insert in the text), so we can where it is? Also if you end by re-inserting your scene with all the domains in color (but perhaps in cartoon?) and use the domain color code in the text of the following paragraph, it would help us to look at the molecule and see the points as you are making them.

The insert domain of the FnIII-2 domain separates the alpha and beta chains of each monomer. The alpha chain contains the L1, CR, L2, FnIII-1 domains and part of the FnIII-2 domain. The beta chain contains the rest of the FnIII-2 domain and the FnIII domain. The insert domain starts and ends with a cleavage site where the chain is cut. The alpha and beta chains are then linked by a single disulphide bond between cysteines C647 and C860, leaving the insert domain as a separate peptide which forms disulphide bonds with cysteines in the FnIII-1 domain. The alpha chain lies completely on the exterior of the cell, while the end of the beta chain extends through the cell membrane and is involved in signaling.

I assume the part of the beta chain that goes through the membrane is not shown? Clarify this if possible. Any further green scenes you can make (or perhaps someone else wants to do them -- you've done quite a few!) could be helpful to show us the disufide link and interactions you mention.

There are few interactions between the two legs of the monomer- just two salt bridges near the connection between the L1 and FnIII-1 domains. However there are many interactions between the two monomers including salt bridges and disulphide bonds. This structure is significant relative to previous structures for the protein because of the relative position of the L1 domains in the two monomers of the biological unit. Unlike in previous structures, the monomers are too far apart to allow binding of one insulin molecule to both L1 domains, as was previously thought.

Do you mean that both halves would not contact the insulin? This could be an interesting point (perhaps move to the binding section), to make with a green scene with a distance marker and compare this distance to the width of the insulin (could measure on insulin structure) if this shows that the V is too wide to contact both sides of insulin.

A

Binding Interactions

The insulin receptor's (IR) main substrate is insulin, which is referred to as insulin receptor substrate 1 (IRS-1). As insulin binds to the IR, the IR is phosphorylated. Phosphorylation of tyrosine residues in the IR leads to an increase in the glucose transporter (Glut-4) which has a high affinity for glucose molecules. This occurs mainly in muscle and adipose (fat) tissues where glucose uptake is most needed. This increase in Glut-4 causes an increase in glucose uptake from blood. Simply stated, 3loh is activated by insulin (IRS-1) which signals for an increase in Glut-4. Glut-4 finds its way to the cell surface where it can perform its function and transport glucose into the cell.

The binding mechanism and site are not completely understood. What is known, however, is that insulin is able to bind at two different locations on each monomer of the insulin receptor. Since there are two monomers in the biologically functional ectodomain, there are in total four locations available for binding and interaction. These locations are explained in the Introduction section of this page. Current literature describes the locations for insulin binding as follows: the region between L1 and Fn2 as site 1, the region involving L2, Fn1, and Fn2 as site 2. Based on knowledge of the structure of the insulin receptor (it is a dimer with mirrored symmetry), one can see that the site 1 of one monomer will be adjacent to site 2 on the other. In order to eliminate confusion, most literature refer to the binding sites across from site 1 and site 2 as site 2' and site 1', respectively ^[6]. Rebecca provided an overview of which domains are important for binding. Can you show us more specific segments/residues implicated in binding? Can 2 insulins bind at the same time? I think with your 1/2' explanation you're telling us that each insulin binds at the dimer interface, yes? Perhaps highlight the 1/2' contact surfaces for one insulin, then the 2/1' interaction surfaces for the 2nd insulin. Or you could work with Rebecca to make this clear in the Introduction where she started to explain it (you can add people to the credits if you work together on sections), and you could focus your Jmol window in the binding section on insulin which is pretty interesting in itself!

Recent research has indicated that it may be possible that both the structure of the insulin receptor and the structure of insulin itself may change upon binding. It is also thought that insulin may posses multiple surfaces that are capable of binding to the functional ectodomain.

Another interesting point to mention is that insulin in its form can also interact with the binding sites available on the insulin receptor. Hexamers of insulin are found in the pancreas and help store insulin. Upon creating the hexameric form, a new binding surface for insulin is created that exhibits normal binding at site 1. Binding does not occur at site 2 however, and thus the hexamer form of insulin does not activate the insulin receptor as does regular form of insulin. Here is a that highlights the second binding surface. The second binding surface is highlighted on one of the three dimers ^[7]. Your color scheme is not working for me; why are there more than 6 colors? Help me to see the hexamer. It would be cool to see the difference in the binding surfaces when insulin is a monomer vs when it is a hexamer. I'm not really following your explanation of this so far -- perhaps highlight binding surfaces on a monomer to show how a new site is created in the hexamer (why? does it involve more than one monomer together creating the binding surface?)

One source believes that the active site for the insulin receptor lies at this , which ranges approximately from Lys1085-Glu1208. The active site is displayed normally with the rest of the monomer faded out. Here is a green scene that depicts the location of the active site for the folded conformation of the insulin receptor. . The active sites are highlighted in green ^[8]. Normally an active site or binding surface is a smaller part of the protein, not a whole domain as you have highlighted here. Is this information available?

Additional Features

Interestingly, the molecular basis as to how binds to the insulin receptor substrate (IRS) remains elusive. However, there has been some light shed on the kinase cascade pathway that insulin induces.

If you want to show us the insulin monomer, please explain the color scheme, and also tell us something about it. It's probably more logical to have all insulin green scenes in one section (, ie the previous section, and you can work together on this).

Recently, studies have shown that poor diet and increased sugar intake have led to a halt in the kinase cascade pathway, leading to what is now termed as insulin resistance.

Insulin Resistance: Happens when the cells essentially don't open the door when insulin comes knocking. When this happens, the body puts out more insulin to stabilize blood glucose in the body. This allows for a vicious cycle where the cells become more and more desensitized as the concentration of insulin increases to tackle the constant influx of glucose. This occurs when the insulin receptor cannot activate the glucose transporter (Glut-4) vesicles to bind to the membrane in order to bring in glucose. ^[9]

Do you mean Glut4? I am confused about IRS: is it insulin that binds to the insulin receptor or the proteins that are phosphorylated by the insulin receptor? Seems like different sections say different things...

Mechanism: When Insulin binds it phosphorylates the IRS, leading to a kinase cascade pathway that ineveitably activates Glut-4 to bind to the cell membrane. Naturally, once the blood glucose has reached a normal level, the kinases are then dephosphorylated, which in turn slowly lower than amount of the glucose channels on the membrane surface. This is the normal negative feedback loop. However, when sugar intake is too high for too long, the amount of stored glucose (glycogen) will reach its maximum capacity. The cell will not take in anymore glucose, which raises blood glucose levels. In response, the Pancreas cranks out insulin in an attempt to lower blood glucose, when the binding interaction with IRS will essentially do nothing. In the end, all of the kinases become stuck in the phosphorylated state from the high concentration of insulin, but no glucose can be stored. The traffic jam will either kill the cell, or if glucose intake recedes, the cell can try to restore itself to its normal feedback loop. ^[10]

So what's the cure?

Extensive research has been conducted to see if the IRS can bind to other proteins which can then induce similar but not the same kinase cascades. The within the receptor homodimer may provide a target for the design of nonpeptide agonists, perhaps achievable in part by molecules the size of antibiotics and could be “druggable.” ^[11] Talk about S519

This is a very interesting point and cool green scene. Can you explain/show any more about this? Why is this a target? Bring the paper to class and talk to me if you want help figuring this out.

Best solution? Eat Healthy! Reducing sugar intake by eating less sweets should cause a break down of excess glycogen, returning cells to normal over time.

Credits

Introduction - Rebecca Bishop

Overall Structure - Kathryn Liedell

Drug Binding Site - Ryan Deeney

Additional Features - Jeffrey Boerth

I suggest that one of you show us what insulin looks like and which are thought to be the binding surfaces on insulin and on the receptor. Prof T -->I think I can work that into the intro. Bec I remember saying I could add the insulin green scene in. If you'd like to add it Bec it's not a big deal, I'd just like to have at least two green scenes. -Jeff I'll also be adding another green scene that involves insulin in my section. I think that we'll all be mentioning it in our sections. - Ryan. Jeff I am pretty happy with my section is, does that duplicate what you wanted to do too much? - Bec

References

1. ↑ Kitamura T, Kahn CR, Accili D. Insulin receptor knockout mice. Annu Rev Physiol. 2003;65:313-32. Epub 2002 May 1. PMID:12471165 doi:10.1146/annurev.physiol.65.092101.142540
2. ↑ Fried R. A literary look at contemporary society. Ohio Med. 1989 May;85(5):393-5. PMID:2657531
3. ↑ Whittaker L, Hao C, Fu W, Whittaker J. High-affinity insulin binding: insulin interacts with two receptor ligand binding sites. Biochemistry. 2008 Dec 2;47(48):12900-9. PMID:18991400 doi:10.1021/bi801693h
4. ↑ Longo N, Wang Y, Smith SA, Langley SD, DiMeglio LA, Giannella-Neto D. Genotype-phenotype correlation in inherited severe insulin resistance. Hum Mol Genet. 2002 Jun 1;11(12):1465-75. PMID:12023989
5. ↑ al-Gazali LI, Khalil M, Devadas K. A syndrome of insulin resistance resembling leprechaunism in five sibs of consanguineous parents. J Med Genet. 1993 Jun;30(6):470-5. PMID:8326490
6. ↑ Ward CW, Lawrence MC. Ligand-induced activation of the insulin receptor: a multi-step process involving structural changes in both the ligand and the receptor. Bioessays. 2009 Apr;31(4):422-34. PMID:19274663 doi:10.1002/bies.200800210
7. ↑ Ward CW, Lawrence MC. Ligand-induced activation of the insulin receptor: a multi-step process involving structural changes in both the ligand and the receptor. Bioessays. 2009 Apr;31(4):422-34. PMID:19274663 doi:10.1002/bies.200800210
8. ↑ Ablooglu AJ, Frankel M, Rusinova E, Ross JB, Kohanski RA. Multiple activation loop conformations and their regulatory properties in the insulin receptor's kinase domain. J Biol Chem. 2001 Dec 14;276(50):46933-40. Epub 2001 Oct 11. PMID:11598120 doi:10.1074/jbc.M107236200
9. ↑ Cusi K, Maezono K, Osman A, Pendergrass M, Patti ME, Pratipanawatr T, DeFronzo RA, Kahn CR, Mandarino LJ. Insulin resistance differentially affects the PI 3-kinase- and MAP kinase-mediated signaling in human muscle. J Clin Invest. 2000 Feb;105(3):311-20. PMID:10675357 doi:10.1172/JCI7535
10. ↑ Zick, Y. Biochemical Society. 2004, 32, 812-816
11. ↑ Smith BJ, Huang K, Kong G, Chan SJ, Nakagawa S, Menting JG, Hu SQ, Whittaker J, Steiner DF, Katsoyannis PG, Ward CW, Weiss MA, Lawrence MC. Structural resolution of a tandem hormone-binding element in the insulin receptor and its implications for design of peptide agonists. Proc Natl Acad Sci U S A. 2010 Apr 13;107(15):6771-6. Epub 2010 Mar 26. PMID:20348418