biology

Protein-S-isoprenylcysteine O-methyltransferase

Protein-S-isoprenylcysteine O-methyltransferase 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 Protein-S-isoprenylcysteine O-methyltransferase rather than just read about it. In short: The isoprenylcysteine o-methyltransferase (EC 2.1.1.100) carries out carboxyl methylation of cleaved eukaryotic proteins that terminate in a CaaX motif. In Saccharomyces cerevisiae (Baker's yeast) this methylation is carried out by Ste14p, an integral endoplasmic reticulum membrane protein.

Key takeaways

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

Reference excerpt

The isoprenylcysteine o-methyltransferase (EC 2.1.1.100) carries out carboxyl methylation of cleaved eukaryotic proteins that terminate in a CaaX motif. In Saccharomyces cerevisiae (Baker's yeast) this methylation is carried out by Ste14p, an integral endoplasmic reticulum membrane protein. Ste14p is the founding member of the isoprenylcysteine carboxyl methyltransferase (ICMT) family, whose members share significant sequence homology. The enzyme catalyzes the chemical reaction

S-adenosyl-L-methionine + protein C-terminal S-farnesyl-L-cysteine ⇌ {\displaystyle \rightleftharpoons } S-adenosyl-L-homocysteine + protein C-terminal S-farnesyl-L-cysteine methyl ester Thus, the two substrates of this enzyme are S-adenosyl methionine and protein C-terminal S-farnesyl-L-cysteine, whereas its two products are S-adenosylhomocysteine and protein C-terminal S-farnesyl-L-cysteine methyl ester.

References

Clarke S, Vogel JP, Deschenes RJ, Stock J (1988). "Posttranslational modification of the Ha-ras oncogene protein: evidence for a third class of protein carboxyl methyltransferases". Proc. Natl. Acad. Sci. U.S.A. 85 (13): 4643–7. Bibcode:1988PNAS...85.4643C. doi:10.1073/pnas.85.13.4643. PMC 280491. PMID 3290900. Ota IM, Clarke S (1989). "Enzymatic methylation of 23-29-kDa bovine retinal rod outer segment membrane proteins. Evidence for methyl ester formation at carboxyl-terminal cysteinyl residues". J. Biol. Chem. 264 (22): 12879–84. doi:10.1016/S0021-9258(18)51569-6. PMID 2753892. Stephenson RC, Clarke S (1990). "Identification of a C-terminal protein carboxyl methyltransferase in rat liver membranes utilizing a synthetic farnesyl cysteine-containing peptide substrate". J. Biol. Chem. 265 (27): 16248–54. doi:10.1016/S0021-9258(17)46215-6. PMID 2398053.

Worked examples

Example 1 — a first encounter with Protein-S-isoprenylcysteine O-methyltransferase

Start with the simplest possible case. Write down what Protein-S-isoprenylcysteine O-methyltransferase 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 Protein-S-isoprenylcysteine O-methyltransferase 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 Protein-S-isoprenylcysteine O-methyltransferase 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 Protein-S-isoprenylcysteine O-methyltransferase

In research: Protein-S-isoprenylcysteine O-methyltransferase 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 Protein-S-isoprenylcysteine O-methyltransferase 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: Protein-S-isoprenylcysteine O-methyltransferase is common in secondary-school and first-year university syllabi. It links to neighbouring topics EC 2.1.1, EC 2.1 stubs, Enzymes of known structure, so understanding it makes those chapters shorter.
In everyday life: Look for Protein-S-isoprenylcysteine O-methyltransferase 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 Protein-S-isoprenylcysteine O-methyltransferase in 20 minutes

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

Frequently asked questions

What is Protein-S-isoprenylcysteine O-methyltransferase in simple terms?

Why does Protein-S-isoprenylcysteine O-methyltransferase 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 Protein-S-isoprenylcysteine O-methyltransferase?

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 Protein-S-isoprenylcysteine O-methyltransferase.