biology

PARL

PARL 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 PARL rather than just read about it. In short: Presenilins-associated rhomboid-like protein, mitochondrial (PSARL), also known as PINK1/PGAM5-associated rhomboid-like protease (PARL), is an inner mitochondrial membrane protein that in humans is encoded by the PARL gene on chromosome 3. It is a member of the rhomboid family of intramembrane serine proteases.

Key takeaways

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

Reference excerpt

Presenilins-associated rhomboid-like protein, mitochondrial (PSARL), also known as PINK1/PGAM5-associated rhomboid-like protease (PARL), is an inner mitochondrial membrane protein that in humans is encoded by the PARL gene on chromosome 3. It is a member of the rhomboid family of intramembrane serine proteases. This protein is involved in signal transduction and apoptosis, as well as neurodegenerative diseases and type 2 diabetes.

Structure Rhomboid family members share a conserved core of six transmembrane helices (TMHs), with the Ser and His residues required to form the catalytic dyad embedded in TMH-4 and TMH-6, respectively. This dyad is found deep below the membrane surface, which indicates that the hydrolysis of peptide bonds occurs within the hydrophobic phospholipid bilayer membrane. As a member of the Parl subfamily, PARL has an additional N-terminal TMH which may form a loop to the catalytic core.

Function This gene encodes a mitochondrial integral membrane protein. Following proteolytic processing of this protein, a small peptide (P-beta) is formed and translocated to the nucleus. This gene may be involved in signal transduction via regulated intramembrane proteolysis of membrane-tethered precursor proteins. Variation in this gene has been associated with increased risk for type 2 diabetes. Alternative splicing results in multiple transcript variants encoding different isoforms. Additionally, PARL is involved in apoptosis through its interactions with the mitochondrial GTPase optic atrophy 1 (OPA1) and the Bcl-2 family-related protein HAX1. OPA1 mainly regulates mitochondrial fusion in the mitochondrial inner membrane, but after proteolytic cleavage by PARL, its short, soluble form contributes to inhibiting apoptosis by slowing down cytochrome c release, and thus, proapoptotic signaling. Alternatively, PARL can inhibit apoptosis by coordinating with HAX1 to activate HtrA2 protease, thus preventing the accumulation of the proapoptotic Bax.

Clinical significance It has been shown that the p.S77N presenilin-associated rhomboid-like protein mutation is not a frequent cause of early-onset Parkinson's disease. Variation in the sequence and/or expression of the gene encoding presenilins-associated rhomboid-like protein (PSARL) may be an important new risk factor for type 2 diabetes and other components of the metabolic syndrome. Mutations in PARL may also be involved in Leber hereditary optic neuropathy by disrupting normal function of the mitochondria, thus promoting retinal ganglion cell death and neurodegeneration.

Interactions PARL has been shown to interact with:

PINK1, OPA1, and HAX1.

References

Illustrations

Worked examples

Example 1 — a first encounter with PARL

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

In research: PARL 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 PARL 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: PARL is common in secondary-school and first-year university syllabi. It links to neighbouring topics Genes on human chromosome 3, Human chromosome 3 gene stubs, Proteins, so understanding it makes those chapters shorter.
In everyday life: Look for PARL 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 PARL in 20 minutes

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

Frequently asked questions

What is PARL in simple terms?

Why does PARL 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 PARL?

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 PARL.