science

L-isoaspartyl methyltransferase

L-isoaspartyl methyltransferase is a science 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 L-isoaspartyl methyltransferase rather than just read about it. In short: Protein L-isoaspartyl methyltransferase (PIMT, PCMT), also called S-adenosyl-L-methionine:protein-L-isoaspartate O-methyltransferase, is an enzyme which recognizes and catalyzes the repair of damaged L-isoaspartyl and D-aspartyl groups in proteins. It is a highly conserved enzyme which is present in nearly all eukaryotes, archaebacteria, and Gram-negative eubacteria.

Key takeaways

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

Reference excerpt

Protein L-isoaspartyl methyltransferase (PIMT, PCMT), also called S-adenosyl-L-methionine:protein-L-isoaspartate O-methyltransferase, is an enzyme which recognizes and catalyzes the repair of damaged L-isoaspartyl and D-aspartyl groups in proteins. It is a highly conserved enzyme which is present in nearly all eukaryotes, archaebacteria, and Gram-negative eubacteria.

Function PIMT acts to transfer methyl groups from S-adenosyl-L-methionine to the alpha side chain carboxyl groups of damaged L-isoaspartyl and D-aspartyl amino acids. The enzyme takes the end methyl residue from the methionine side chain and adds it to the side chain carboxyl group of L-isoaspartate or D-aspartate to create a methyl ester. Subsequent nonenzymatic reactions result in a rapid transformation to L-succinimide, which is a precursor to aspartate and isoaspartate. The L-succinimide can then undergo nonenzymatic hydrolysis, which generates some repaired L-aspartyl residues as well as some L-isoaspartyl residues, which can then enter the cycle again for eventual conversion to the normal peptide linkage. PIMT tends to act on proteins that have been non-enzymatically damaged due to age. By performing this repair mechanism, the enzyme helps to maintain overall protein integrity. This mechanism has been observed by several groups, and has been confirmed through experimental testing. In one report, PIMT was inhibited by adenosine dialdehyde. The results supported the proposed function of the enzyme, as the amount of abnormal L-aspartate residues increased when cells were treated with the indirect inhibitor, adenosine dialdehyde. Additionally, S-adenosylhomocysteine is known to be a competitive inhibitor of PIMT. When PIMT is not present in cells, the abnormal aspartyl residues accumulate, creating abnormal proteins that have been known to cause fatal progressive epilepsy in mice. It has been suggested that calmodulin may play a role in stimulating the function of PIMT, although the relationship between these two molecules has not been thoroughly explored. In addition to calmodulin, guanosine 5'-O-[gamma-thio]triphosphate (GTPgammaS) has been found to stimulate PIMT activity.

Structure The enzyme is present in human cytosol in two forms due to alternative splicing and differs among individuals in the population due to a single polymorphism at residue 119, either valine or isoleucine. The enzyme structure is described as a “doubly wound alpha/beta/alpha sandwich structure” which is quite consistent in all species analyzed thus far. If there is any difference in the sequences between different organisms it occurs in the regions connecting the three motifs in the sandwich structure, but the sequence of the individual motifs tends to be highly conserved. Researchers have found the active site to be in the loop between the beta structure and the second alpha helix and have determined it to be highly specific for isoaspartyl residues. For example, the residues found at the C-terminus of drosophila PIMT (dPIMT) are rotated 90 degrees so as to allow more space for a substrate to interact with the enzyme. In fact, dPIMT appears to alternate between this unique open conformation and the less open conformation common of PIMT in other organisms. Although possibly unrelated to this, increased levels of dPIMT in drosophila have been correlated with increase life expectancy in these organisms due to their importance in protein repair.

Reaction

See also methyltransferase isoaspartate aspartic acid

External links EC 2.1.1.77 Enzyme Entry On ProteinDatabank

References

Illustrations

Worked examples

Example 1 — a first encounter with L-isoaspartyl methyltransferase

Start with the simplest possible case. Write down what L-isoaspartyl methyltransferase claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 L-isoaspartyl 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 L-isoaspartyl 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 L-isoaspartyl methyltransferase

In research: L-isoaspartyl methyltransferase appears in science 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 L-isoaspartyl 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: L-isoaspartyl methyltransferase is common in secondary-school and first-year university syllabi. It links to neighbouring topics EC 2.1.1, Enzymes, so understanding it makes those chapters shorter.
In everyday life: Look for L-isoaspartyl 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 L-isoaspartyl methyltransferase in 20 minutes

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

Frequently asked questions

What is L-isoaspartyl methyltransferase in simple terms?

Why does L-isoaspartyl methyltransferase matter?

Because it connects several science 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 L-isoaspartyl 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 L-isoaspartyl methyltransferase.