biology

GPR55

GPR55 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 GPR55 rather than just read about it. In short: G protein-coupled receptor 55 also known as GPR55 is a G protein-coupled receptor that in humans is encoded by the GPR55 gene. GPR55, along with GPR119 and GPR18, have been implicated as novel cannabinoid receptors.

Key takeaways

GPR55 belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect GPR55 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of GPR55 from memory before moving on to harder problems.

Reference excerpt

G protein-coupled receptor 55 also known as GPR55 is a G protein-coupled receptor that in humans is encoded by the GPR55 gene. GPR55, along with GPR119 and GPR18, have been implicated as novel cannabinoid receptors.

History GPR55 was identified and cloned for the first time in 1999. Later it was identified by an in silico screen as a putative cannabinoid receptor because of a similar amino acid sequence in the binding region. Research groups from Glaxo Smith Kline and Astra Zeneca characterized the receptor extensively because it was hoped to be responsible for the blood pressure lowering properties of cannabinoids. GPR55 is indeed activated by endogenous and exogenous cannabinoids such as plant and synthetic cannabinoids but GPR-55 knockout mice generated by a research group from Glaxo Smith Kline showed no altered blood pressure regulation after administration of the cannabidiol-derivative abnormal cannabidiol.

Signal cascade GPR55 is coupled to the G-protein G13 and activation of the receptor leads to stimulation of rhoA, cdc42 and rac1.

Pharmacology GPR55 is acted on by the phytocannabinoids Δ9-THC and CBD, as well as the endocannabinoids anandamide, 2-AG and noladin ether in the low nanomolar range. Exocannabinoids such as the synthetic cannabinoid CP-55940 are also able to activate the receptor while the structurally unrelated cannabinoid mimic WIN 55,212-2 fails to activate the receptor. Recent research suggests that lysophosphatidylinositol and its 2-arachidonoyl derivative, 2-arachidonoyl lysophosphatidylinositol (2-ALPI), may be the endogenous ligands for GPR55 and the receptor appears likely to be a possible target for treatment of inflammation and pain as with the other cannabinoid receptors. This profile as a distinct non-CB1/CB2 receptor which responds to a variety of both endogenous and exogenous cannabinoid ligands has led some groups to suggest GPR55 should be categorised as the CB3 receptor, and this re-classification may follow in time. However this is complicated by the fact that another possible CB3 receptor has been discovered in the hippocampus, although its gene has not yet been cloned, suggesting that there may be at least four cannabinoid receptors which will eventually be characterised. Evidence accumulated during the last few years suggests that GPR55 plays a relevant role in cancer and opens the possibility of considering this orphan receptor as a new therapeutic target and potential biomarker in oncology.

Ligands Agonists Ligands found to bind to GPR55 as agonists include:

Lysophosphatidylinositol 2-Arachidonoyl lysophosphatidylinositol Abnormal cannabidiol (Abn-CBD) AM-251 (also CB1 antagonist) CP 55,940 GSK-319,197 GSK-494,581 - also glycine transporter 1 inhibitor GSK-522,373 O-1602 Δ9-Tetrahydrocannabinol Tetrahydrocannabivarin (THCV) 2-Arachidonoylglycerol (2-AG) Noladin ether Oleoylethanolamide Palmitoylethanolamide PACAP ML-184, ML-185 and ML-186 Antagonists CID-16020046 - inverse agonist at GPR55 O-1918 ML-191, ML-192 and ML-193 PSB-SB-487 and PSB-SB-1203 Cannabidiol KLS-13019

Physiological function The physiological role of GPR55 is unclear. Mice with a target deletion of the GPR55 gene show no specific phenotype. GPR55 is widely expressed in the brain, especially in the cerebellum. It is expressed in the jejunum and ileum but apparently not more generally in the periphery. Osteoblasts and osteoclasts express GPR55 and this has been shown to regulate bone cell function.

References

Illustrations

Worked examples

Example 1 — a first encounter with GPR55

Start with the simplest possible case. Write down what GPR55 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 GPR55 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 GPR55 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 GPR55

In research: GPR55 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 GPR55 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: GPR55 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 GPR55 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 GPR55 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what GPR55 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.
Explain GPR55 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is GPR55 in simple terms?

Why does GPR55 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 GPR55?

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 GPR55.