Telokin

Key takeaways

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

Reference excerpt

Telokin (also known as kinase-related protein or KRP) is an abundant protein found in smooth-muscle. It is identical to the C-terminus of myosin light-chain kinase. Telokin may play a role in the stabilization of unphosphorylated smooth-muscle myosin filaments. Because of its origin as the C-terminal end of smooth muscle myosin light chain kinase, it is called "telokin" (from a combination of the Greek telos, "end" and kinase).

Nomenclature and classification Telokin's systematic name is ATP:[myosin light chain] O-phosphotransferase and its recommended name is myosin-light-chain kinase. (EC 2.7.11.18). The gene MYLK, a muscle member of the immunoglobulin gene superfamily, encodes myosin light chain kinase which is a calcium/calmodulin dependent enzyme. Four transcript variants that produce four isoforms of the calcium/calmodulin dependent enzyme have been identified as well as two transcripts that produce two isoforms of telokin. The two transcripts that produce the two telokin isoforms are the following:

Isoform 7 This variant encodes the shorter isoform of kinase related protein, telokin. The first exon corresponds to intron 30 and the remainder of the transcript corresponds to the last two exons of the gene. It is shorter than variant 8 by one codon at the splicing junction between the first two exons. It is made by 153 aa. NCBI Reference Sequence: NP_444259.1. It comes from the Homo sapiens myosin light chain kinase (MYLK), transcript variant 7, mRNA, whose length is 2676 bp. NCBI Reference Sequence: NM_053031.2. Isoform 8 This variant encodes the longer isoform of kinase related protein, telokin. It is longer than variant 7 by one codon at the splicing junction between the first two exons. It is composed of 154 aa. NCBI Reference Sequence: NP_444260.1. It comes from the Homo sapiens myosin light chain kinase (MYLK), transcript variant 8, mRNA, whose length is 2679 bp. NCBI Reference Sequence: NM_053032.2.

Catalytic activity and other functional data Telokin catalyzes the following reaction:

ATP + myosin-light-chain = ADP + myosin-light-chain phosphate. (Reaction type: phospho group transfer) It requires Ca2+ and calmodulin for activity. The 20-kDa light chain from smooth muscle myosin is phosphorylated more rapidly than any other acceptor, but light chains from other myosins and myosin itself can act as acceptors, but more slowly. The Km values of homo sapiens telokin is 0.018 mM at 23–25 °C and pH = 7.5. This enzyme has a pH optimum of 7.4 and temperature optimum of 30 °C. Telokin is an acidic protein with a PI value of 4-5 and 17-kDa with an amino acid sequence that is identical to the C terminus of the 130-kDa myosin light chain kinase (MLCK), although it is expressed as a separate protein and produced by an alternate promoter of the MLCK gene. Telokin is transcribed from a second promoter, located within an intron, in the 3' region of the MLCK gene. And that is why the concentration of telokin (at least 15 μM) is higher than MLCK concentration. Telokin has been shown to bind to unphosphorylated myosin filaments and to stimulate myosin mini-filament assembly in vitro. The major mechanism for initiating smooth muscle (SM)2 contraction is the rise in Ca2+ concentration resulting in an increase in 20-kDa myosin regulatory light chain (MLC20) phosphorylation at Ser-19.

Structure Primary structure Telokin is an intracellular protein and, as such, does not contain the disulfide linkage between beta-strands B and F normally observed in the immunoglobulin constant domains. It does, however, contain two cysteine amino acid residues (Cys63 and Cys115) that are situated at structurally identical positions to those forming the disulfide linkage in the immunoglobulin constant domain. Secondary structure Telokin contains 154 amino acid residues, 103 of which were visible in the electron density map. Telokin and the C-terminal domain of MLCK show amino acid sequence similarity to several quite unrelated muscle proteins such as titin or C-protein. The overall molecular fold of telokin consists of seven strands of antiparallel beta-pleated sheet that wrap around to form a barrel. There is also an extended tail of eight amino acid residues at the N terminus that does not participate in beta-sheet formation. The beta-barrel can be simply envisioned as two layers of beta-sheet, nearly parallel to one another, with one layer containing four and the other three beta-strands. Domains Telokin has a particular domain called Ig-like I-type (Immunoglobulin like intermediate type) with a length of 92 residues between 42 and 133. At the beginning it was thought that this domain was Ig- like C2-type but some studies determined that its structure shares characteristics from V-set and C2-set and that is why the a I-type was invented. These kind of domains mediates T-cell adhesion via its ectodomain, and signal transduction.[2]

Tissue distribution KRP presence in different tissues has been assessed by immunoblots using anti-KRP antibodies, and by analyses of its mRNA in Northern blot. KRP is an abundant smooth muscles-pecific protein. So far it has not been detected in non-muscle tissues and striated muscles. Its concentration in gizzard muscle is lo-12-fold higher than that of MLCK and only 2-3-fold less than that of myosin. Vascular muscles have a lower KRP/MLCK ratio. Telokin is expressed at very high levels in intestinal, urinary, and reproductive tract smooth muscle, at lower levels in vascular smooth muscle, and at undetectable levels in skeletal or cardiac muscle or nonmuscle tissues. Although telokin is strongly activated by myocardin and myocardin is highly expressed in vascular smooth muscle cells, there is relatively little expression of telokin in these cells. This suggests that an inhibitory factor must be attenuating the activity of the telokin promoter in vascular smooth muscle cells. One possible candidate for this inhibitory factor is GATA-6 The increase in telokin expression correlated with an increase in the expression of several other smooth muscle-restricted proteins, including smooth muscle myosin and alpha-actin. Accumulates in individuals with asthma (at protein levels). Induced by tumor necrosis factor (TNF). Repressed by androgens (e.g. R1881).

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Telokin

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

In research: Telokin 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 Telokin 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: Telokin is common in secondary-school and first-year university syllabi. It links to neighbouring topics Genes on human chromosome 3, Human genes, Motor proteins, so understanding it makes those chapters shorter.
In everyday life: Look for Telokin 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.

How to study Telokin in 20 minutes

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

Frequently asked questions

What is Telokin in simple terms?

Telokin (also known as kinase-related protein or KRP) is an abundant protein found in smooth-muscle. It is identical to the C-terminus of myosin light-chain kinase.

Why does Telokin 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 Telokin?

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 Telokin.