biology

XPNPEP3

XPNPEP3 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 XPNPEP3 rather than just read about it. In short: Xaa-Pro aminopeptidase 3, also known as aminopeptidase P3, is an enzyme that in humans is encoded by the XPNPEP3 gene. XPNPEP3 localizes to mitochondria in renal cells and to kidney tubules in a cell type-specific pattern.

Key takeaways

XPNPEP3 belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect XPNPEP3 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of XPNPEP3 from memory before moving on to harder problems.

Reference excerpt

Xaa-Pro aminopeptidase 3, also known as aminopeptidase P3, is an enzyme that in humans is encoded by the XPNPEP3 gene. XPNPEP3 localizes to mitochondria in renal cells and to kidney tubules in a cell type-specific pattern. Mutations in XPNPEP3 gene have been identified as a cause of a nephronophthisis-like disease.

Structure

Gene The XPNPEP3 gene is located at chromosome 22q13.2, consisting of 12 exons. Two splice variants of XPNPEP3, APP3m and APP3c, exist in mitochondria and cytosol, respectively.

Protein APP3m has an N-terminal mitochondrial-targeting sequence (MTS) domain importing APP3m into mitochondria, where the domain is removed proteolytically and APP3m functions as a 51-kDa mature protein. By contrast, APP3c, lacks the MTS and is expressed in the cytosol. Arginine in MTS is required for mitochondrial transport.

Function XPNPEP3 belongs to a family of X-pro-aminopeptidases (EC 3.4.11.9) that utilize a metal cofactor and remove the N-terminal amino acid from peptides with a proline residue in the penultimate position. It has been found that upon tumor necrosis factor stimulation, XPNPEP3 is released from mitochondria. XPNPEP3 is a new member of the TNF-TNFR2 signaling complex and plays a role in the transduction mechanism of TNFR2 signal which activates both JNK1 and JNK2 pathways. It is also observed that cell death increases upon downregulation of XPNPEP3, suggesting XPNPEP3 exerts an anti-apoptotic function. Deletion of icp55, the S. cerevisiae ortholog of XPNPEP3, increases the proteolytic rate of its substrates through a protein degradation pathway characterized by the N-end rule.

Clinical significance Mutations in the XPNPEP3 gene are associated with ciliopathy. Recessive mutations in XPNPEP3 gene has been identified as a cause of a nephronophthisis-like disease, characterized by renal interstitial infiltration with fibrosis, tubular atrophy with basement membrane disruption, and cyst development at the corticomedullary renal border. Phenotypic variability might be ascribed to different degrees of loss of function for the 2 different homozygous XPNPEP3 alleles. The ciliary phenotypes unmasked by loss of XPNPEP3 might arise from the loss of XPNPEP3-dependent processing of ciliary proteins.

Interactions NPHP6/CEP290 TNF

References

Worked examples

Example 1 — a first encounter with XPNPEP3

Start with the simplest possible case. Write down what XPNPEP3 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 XPNPEP3 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 XPNPEP3 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 XPNPEP3

In research: XPNPEP3 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 XPNPEP3 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: XPNPEP3 is common in secondary-school and first-year university syllabi. It links to neighbouring topics EC 3.4.11, Human chromosome 22 gene stubs, so understanding it makes those chapters shorter.
In everyday life: Look for XPNPEP3 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 XPNPEP3 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what XPNPEP3 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 XPNPEP3 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is XPNPEP3 in simple terms?

Why does XPNPEP3 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 XPNPEP3?

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 XPNPEP3.