biology

S-Adenosylmethionine synthetase

S-Adenosylmethionine synthetase 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 S-Adenosylmethionine synthetase rather than just read about it. In short: S-Adenosylmethionine synthetase (EC 2.5.1.6), also known as methionine adenosyltransferase (MAT), is an enzyme that creates S-adenosylmethionine (also known as AdoMet, SAM or SAMe) by reacting methionine (a non-polar amino acid) and ATP (the basic currency of energy). Three types of MAT have been identified in mammals, and are denoted MAT I, II, and III.

Key takeaways

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

Reference excerpt

S-Adenosylmethionine synthetase (EC 2.5.1.6), also known as methionine adenosyltransferase (MAT), is an enzyme that creates S-adenosylmethionine (also known as AdoMet, SAM or SAMe) by reacting methionine (a non-polar amino acid) and ATP (the basic currency of energy). Three types of MAT have been identified in mammals, and are denoted MAT I, II, and III. MAT I (resp. III) is composed of 4 (resp. 2) copies of the protein subunit coded by the gene MAT1A, while MAT II is a more complicated complex of the subunits coded by MAT2A and MAT2B.

Function AdoMet is a methyl donor for transmethylation. It gives away its methyl group and is also the propylamino donor in polyamine biosynthesis. S-adenosylmethionine synthesis can be considered the rate-limiting step of the methionine cycle. As a methyl donor SAM allows DNA methylation. Once DNA is methylated, it switches the genes off and therefore, S-adenosylmethionine can be considered to control gene expression. SAM is also involved in gene transcription, cell proliferation, and production of secondary metabolites. Hence SAM synthetase is fast becoming a drug target, in particular for the following diseases: depression, dementia, vacuolar myelopathy, liver injury, migraine, osteoarthritis, and as a potential cancer chemopreventive agent. This article discusses the protein domains that make up the SAM synthetase enzyme and how these domains contribute to its function. More specifically, this article explores the shared pseudo-3-fold symmetry that makes the domains well-adapted to their functions. This enzyme catalyses the following chemical reaction

ATP + L-methionine + H2O ⇌ {\displaystyle \rightleftharpoons } phosphate + diphosphate + S-adenosyl-L-methionine

Conserved motifs in the 3'UTR of MAT2A mRNA A computational comparative analysis of vertebrate genome sequences have identified a cluster of 6 conserved hairpin motifs in the 3'UTR of the MAT2A messenger RNA (mRNA) transcript. The predicted hairpins (named A-F) have strong evolutionary conservation and 3 of the predicted RNA structures (hairpins A, C and D) have been confirmed by in-line probing analysis. No structural changes were observed for any of the hairpins in the presence of metabolites SAM, S-adenosylhomocysteine or L-Methionine. They are proposed to be involved in transcript stability and their functionality is currently under investigation.

Protein overview The S-adenosylmethionine synthetase enzyme is found in almost every organism bar parasites which obtain AdoMet from their host. Isoenzymes are found in bacteria, budding yeast and even in mammalian mitochondria. Most MATs are homo-oligomers and the majority are tetramers. The monomers are organised into three domains formed by nonconsecutive stretches of the sequence, and the subunits interact through a large flat hydrophobic surface to form the dimers.

S-adenosylmethionine synthetase N terminal domain

In molecular biology the protein domain S-adenosylmethionine synthetase N terminal domain is found at the N-terminal of the enzyme.

N terminal domain function The N terminal domain is well conserved across different species. This may be due to its important function in substrate and cation binding. The residues involved in methionine binding are found in the N-terminal domain.

N terminal domain structure The N terminal region contains two alpha helices and four beta strands.

S-adenosylmethionine synthetase Central domain

Central terminal domain function The precise function of the central domain has not been fully elucidated, but it is thought to be important in aiding catalysis.

Central domain structure The central region contains two alpha helices and four beta strands.

S-adenosylmethionine synthetase, C terminal domain

In molecular biology, the protein domain S-adenosylmethionine synthetase, C-terminal domain refers to the C terminus of the S-adenosylmethionine synthetase

C terminal domain function The function of the C-terminal domain has been experimentally determined as being important for cytoplasmic localisation. The residues are scattered along the C-terminal domain sequence however once the protein folds, they position themselves closely together.

C terminal domain structure The C-terminal domains contains two alpha-helices and four beta-strands.

References

External links Methionine+adenosyltransferase at the U.S. National Library of Medicine Medical Subject Headings (MeSH) EC 2.5.1.6

Illustrations

Worked examples

Example 1 — a first encounter with S-Adenosylmethionine synthetase

Start with the simplest possible case. Write down what S-Adenosylmethionine synthetase 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 S-Adenosylmethionine synthetase 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 S-Adenosylmethionine synthetase 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 S-Adenosylmethionine synthetase

In research: S-Adenosylmethionine synthetase 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 S-Adenosylmethionine synthetase 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: S-Adenosylmethionine synthetase is common in secondary-school and first-year university syllabi. It links to neighbouring topics EC 2.5.1, Enzymes, Gene expression, so understanding it makes those chapters shorter.
In everyday life: Look for S-Adenosylmethionine synthetase 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 S-Adenosylmethionine synthetase in 20 minutes

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

Frequently asked questions

What is S-Adenosylmethionine synthetase in simple terms?

Why does S-Adenosylmethionine synthetase 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 S-Adenosylmethionine synthetase?

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 S-Adenosylmethionine synthetase.