biology

KH domain

KH domain 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 KH domain rather than just read about it. In short: The K Homology (KH) domain is a protein domain that was first identified in the human heterogeneous nuclear ribonucleoprotein (hnRNP) K. An evolutionarily conserved sequence of around 70 amino acids, the KH domain is present in a wide variety of nucleic acid-binding proteins.

Key takeaways

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

Reference excerpt

The K Homology (KH) domain is a protein domain that was first identified in the human heterogeneous nuclear ribonucleoprotein (hnRNP) K. An evolutionarily conserved sequence of around 70 amino acids, the KH domain is present in a wide variety of nucleic acid-binding proteins. The KH domain binds RNA, and can function in RNA recognition. It is found in multiple copies in several proteins, where they can function cooperatively or independently. For example, in the AU-rich element RNA-binding protein KSRP, which has 4 KH domains, KH domains 3 and 4 behave as independent binding modules to interact with different regions of the AU-rich RNA targets. The solution structure of the first KH domain of FMR1 and of the C-terminal KH domain of hnRNP K determined by nuclear magnetic resonance (NMR) revealed a beta-alpha-alpha-beta-beta-alpha structure. Autoantibodies to NOVA1, a KH domain protein, cause paraneoplastic opsoclonus ataxia. The KH domain is found at the N-terminus of the ribosomal protein S3. This domain is unusual in that it has a different fold compared to the normal KH domain.

Nucleic acid binding KH domains bind to either RNA or single stranded DNA. The nucleic acid is bound in an extended conformation across one side of the domain. The binding occurs in a cleft formed between alpha helix 1, alpha helix 2 the GXXG loop (contains a highly conserved sequence motif) and the variable loop. The binding cleft is hydrophobic in nature with a variety of additional protein specific interactions to stabilise the complex. Valverde and colleagues note that, "Nucleic acid base-to-protein aromatic side chain stacking interactions which are prevalent in other types of single stranded nucleic acid binding motifs, are notably absent in KH domain nucleic acid recognition".

Structural groups

Structurally there are two different types of KH domains identified by Grishin which are called type I and type II. The type I domains are mainly found in eukaryotic proteins, while the type II domains are predominantly found in prokaryotes. While both types share a minimal consensus sequence motif they have different structural folds. The type I KH domains have a three stranded beta-sheet where all three strands are anti-parallel. In the type II domain two of the three beta strands are in a parallel orientation. While type I domains are usually found in multiple copies within proteins, the type II are typically found in a single copy per protein.

Human proteins containing this domain AKAP1; ANKHD1; ANKRD17; ASCC1; BICC1; DDX43; DDX53; DPPA5; ERAL1; FMR1; FUBP1; FUBP3; FXR1; FXR2; GLD1; HDLBP; HNRPK; IGF2BP1; IGF2BP2; IGF2BP3; KHDRBS1; KHDRBS2; KHDRBS3; KHSRP; KRR1; MEX3A; MEX3B; MEX3C; MEX3D; NOVA1; NOVA2; PCBP1; PCBP2; PCBP3; PCBP4; PNO1; PNPT1; QKI; SF1; TDRKH;

References

Illustrations

Worked examples

Example 1 — a first encounter with KH domain

Start with the simplest possible case. Write down what KH domain 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 KH domain 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 KH domain 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 KH domain

In research: KH domain 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 KH domain 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: KH domain is common in secondary-school and first-year university syllabi. It links to neighbouring topics Protein domains, Protein superfamilies, so understanding it makes those chapters shorter.
In everyday life: Look for KH domain 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 KH domain in 20 minutes

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

Frequently asked questions

What is KH domain in simple terms?

Why does KH domain 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 KH domain?

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 KH domain.