biology

Methyl-accepting chemotaxis proteins

Methyl-accepting chemotaxis proteins 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 Methyl-accepting chemotaxis proteins rather than just read about it. In short: The methyl-accepting chemotaxis proteins (MCP, also aspartate receptor) are a family of transmembrane receptors that mediate chemotactic response in certain enteric bacteria, such as Salmonella enterica enterica and Escherichia coli. These methyl-accepting chemotaxis receptors are one of the first components in the sensory excitation and adaptation responses in bacteria, which act to alter swimming behaviour upon de…

Key takeaways

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

Reference excerpt

The methyl-accepting chemotaxis proteins (MCP, also aspartate receptor) are a family of transmembrane receptors that mediate chemotactic response in certain enteric bacteria, such as Salmonella enterica enterica and Escherichia coli. These methyl-accepting chemotaxis receptors are one of the first components in the sensory excitation and adaptation responses in bacteria, which act to alter swimming behaviour upon detection of specific chemicals. Use of the MCP allows bacteria to detect concentrations of molecules in the extracellular matrix so that the bacteria may smooth swim or tumble accordingly. If the bacterium detects rising levels of attractants (nutrients) or declining levels of repellents (toxins), the bacterium will continue swimming forward, or smooth swimming. If the bacterium detects declining levels of attractants or rising levels of repellents, the bacterium will tumble and re-orient itself in a new direction. In this manner, a bacterium may swim towards nutrients and away from toxins.

Evolution There are many different types of bacterial 60 kDa transmembrane receptors, which share similar topology and signalling mechanisms. They possess three domains: a periplasmic ligand-binding domain, two transmembrane segments, and a cytoplasmic domain. The structure of the ligand-binding domain comprises a closed or partly opened, four-helical bundle with a left-handed twist. The difference in the sequence of the ligand-binding domain between receptors reflects the different ligand specificities. Binding of the ligand causes a conformational change that is transmitted across the membrane to the cytoplasmic activation domain. Environmental diversity gives rise to diversity in bacterial signalling receptors, and consequently there are many genes encoding MCPs. For example, there are four well-characterised MCPs found in Escherichia coli: Tar (taxis towards aspartate and maltose, away from nickel and cobalt), Tsr (taxis towards serine, away from leucine, indole and weak acids), Trg (taxis towards galactose and ribose) and Tap (taxis towards dipeptides).

Structure MCPs share similar structure and signalling mechanism. MCPs form dimers. Three dimers of MCP spontaneously form trimers. Trimers are complexed by CheA and CheW into hexagonal lattices. MCPs either bind ligands directly or interact with ligand-binding proteins, transducing the signal to downstream signalling proteins in the cytoplasm. Most MCPs contain: (a) an N-terminal signal peptide that is a transmembrane alpha-helix in the mature protein; (b) a poorly-conserved periplasmic receptor (ligand-binding) domain; (c) a transmembrane alpha-helix; (d) generally one or more HAMP domains and (e) a highly conserved C-terminal cytoplasmic domain that interacts with downstream signalling components. The C-terminal domain contains the methylated glutamate residues. MCPs undergo two covalent modifications: deamidation and reversible methylation at a number of glutamate residues. Attractants increase the level of methylation, while repellents decrease it. The methyl groups are added by the methyl-transferase CheR and are removed by the methylesterase CheB.

Function Binding a ligand causes a conformational change in the MCP receptor which translates down the hairpin structure and inhibits its sensor kinase. At the tip of the hairpin are two proteins that associate to the MCP: CheW and CheA. CheA acts as the sensor kinase. CheA has kinase activity and autophosphorylates itself on a histidyl residue when activated by the MCP. CheW is believed to be a transducer of the signal from the MCP to CheA. Activated CheA transfers its phosphoryl group to CheY, a response regulator. Phosphorylated CheY phosphorylates the basal body FliM which is connected to the flagellum. Phosphorylation of the basal body acts as a flagellar switch and changes the direction of rotation of the flagellum. This change in direction allows for alternation between smooth swimming and tumbling which biases the bacterial random walk towards attractant.

References

Illustrations

Worked examples

Example 1 — a first encounter with Methyl-accepting chemotaxis proteins

Start with the simplest possible case. Write down what Methyl-accepting chemotaxis proteins 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 Methyl-accepting chemotaxis proteins 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 Methyl-accepting chemotaxis proteins 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 Methyl-accepting chemotaxis proteins

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

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

Frequently asked questions

What is Methyl-accepting chemotaxis proteins in simple terms?

Why does Methyl-accepting chemotaxis proteins 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 Methyl-accepting chemotaxis proteins?

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 Methyl-accepting chemotaxis proteins.