biology

G protein-coupled bile acid receptor

G protein-coupled bile acid receptor is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand G protein-coupled bile acid receptor rather than just read about it. In short: The G protein-coupled bile acid receptor 1 (GPBAR1) also known as G-protein coupled receptor 19 (GPCR19), membrane-type receptor for bile acids (M-BAR) or Takeda G protein-coupled receptor 5 (TGR5) is a protein that in humans is encoded by the GPBAR1 gene. Activated by bile acids, these receptors play a crucial role in metabolic regulation, including insulin secretion and energy balance, and are found in the gastroi…

Key takeaways

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Reproduce the core statement of G protein-coupled bile acid receptor from memory before moving on to harder problems.

Reference excerpt

The G protein-coupled bile acid receptor 1 (GPBAR1) also known as G-protein coupled receptor 19 (GPCR19), membrane-type receptor for bile acids (M-BAR) or Takeda G protein-coupled receptor 5 (TGR5) is a protein that in humans is encoded by the GPBAR1 gene. Activated by bile acids, these receptors play a crucial role in metabolic regulation, including insulin secretion and energy balance, and are found in the gastrointestinal tract as well as other tissues throughout the body.

History TGR5 receptors were first discovered by Takaharu Maruyama in 2002. It was the first membrane bound G protein coupled receptor that was discovered for faster bile acid signaling. Initially, up until the late 90's, bile acids were known only for its metabolic function of emulsifying fats and keeping cholesterol homeostasis. It wasn't until 1999 when researchers began exploring into its role as a hormone and signaling molecule with the discovery of the nuclear bile acid receptors, Farnesoid X Receptors (FXR).

Location TGR5 receptors are primarily located in gastrointestinal tracts where bile acid functions are most prevalent. They can also be found throughout the body, including the nervous system, immune system, and various muscle groups, aiding in the tasks that are relevant to their respective locations.

Function

The primary function of the TGR5 receptor is for the binding of bile acid to elicit second messenger systems in the metabolic role of bile acids. It is also a receptor for other agonists, including activating various other pathways responsible for responses like inflammation. TGR5 receptors are a member of the G protein-coupled receptor (GPCR) superfamily. As mentioned, this protein functions as a cell surface receptor for bile acids. Treatment of cells expressing this GPCR with bile acids induces the production of intracellular cAMP, activation of a MAP kinase signaling pathway, and internalization of the receptor. The receptor is implicated in the suppression of macrophage functions and regulation of energy homeostasis by bile acids. One effect of this receptor is to activate deiodinases which convert the prohormone thyroxine (T4) to the active hormone triiodothyronine (T3). T3 in turn activates the thyroid hormone receptor which increases metabolic rate.

Bile Acid Effects on TGR5 Bile acid binds to the TGR5 receptor which increases the secretion of GLP-1. GLP-1 increases glucose-induced insulin secretion, satiety, and pancreatic beta cell production (responsible for insulin secretion). GLP-1 is also used in medications to treat type 2 diabetes. GLP-1 undergoes heightened production through 2 pathways. The first pathway is the activation of Adenylyl cyclase and cAMP which begins a secondary messenger cascade to release GLP-1. The second pathway entails the increase in mitochondrial activity in response to nutrients like glucose and fatty acids which causes an increase in the ATP to ADP ratio. This leads to the inactivation of ATP-sensitive potassium channels that causes the cell membrane to depolarize. This depolarization causes an increase in voltage-gated calcium channel activity, sending a flood of calcium ions which triggers a cascade of events leading to increased GLP-1 secretion.

Extraintestinal Activation of TGR5 Receptors by Bile Acids Bile acid's ability to act as an antagonist for TGR5 receptors located outside of the gastrointestinal tract means it has the ability to escape the tract and travel to these various regions. Primary bile acids are synthesized by hepatocytes in the liver and get conjugated with taurine or glycine before they are stored in the gall bladder for stimulated secretion. Upon the presence of fats and proteins in the duodenum from the diet, these primary bile acids get secreted into the intestine where they are converted into secondary bile acids. 95% of these bile acids get reabsorbed into the liver for recirculation, of which 10% escapes this enterohepatic circulation and enters the systemic circulation. It is through their presence in the serum that they are able to get to various other organs where transporters and channels located at their membranes and barriers allow them to access the TGR5 receptors.

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References

Illustrations

Worked examples

Example 1 — a first encounter with G protein-coupled bile acid receptor

Start with the simplest possible case. Write down what G protein-coupled bile acid receptor claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to G protein-coupled bile acid receptor before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about G protein-coupled bile acid receptor ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of G protein-coupled bile acid receptor

In research: G protein-coupled bile acid receptor appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses G protein-coupled bile acid receptor in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: G protein-coupled bile acid receptor is common in secondary-school and first-year university syllabi. It links to neighbouring topics G protein-coupled receptors, Genes on human chromosome 2, so understanding it makes those chapters shorter.
In everyday life: Look for G protein-coupled bile acid receptor outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study G protein-coupled bile acid receptor in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what G protein-coupled bile acid receptor means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
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Frequently asked questions

What is G protein-coupled bile acid receptor in simple terms?

Why does G protein-coupled bile acid receptor matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study G protein-coupled bile acid receptor?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on G protein-coupled bile acid receptor.