chemistry

Lactonase

Lactonase is a chemistry 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 Lactonase rather than just read about it. In short: Lactonase (EC 3.1.1.81, acyl-homoserine lactonase; systematic name N-acyl-L-homoserine-lactone lactonohydrolase) is a metalloenzyme, produced by certain species of bacteria, which targets and inactivates acylated homoserine lactones (AHLs). It catalyzes the reaction an N-acyl-L-homoserine lactone + H2O ⇌ {\displaystyle \rightleftharpoons } an N-acyl-L-homoserine Many species of α-, β-, and γ-proteobacteria produce a…

Key takeaways

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

Reference excerpt

Lactonase (EC 3.1.1.81, acyl-homoserine lactonase; systematic name N-acyl-L-homoserine-lactone lactonohydrolase) is a metalloenzyme, produced by certain species of bacteria, which targets and inactivates acylated homoserine lactones (AHLs). It catalyzes the reaction

an N-acyl-L-homoserine lactone + H2O ⇌ {\displaystyle \rightleftharpoons } an N-acyl-L-homoserine Many species of α-, β-, and γ-proteobacteria produce acylated homoserine lactones, small hormone-like molecules commonly used as communication signals between bacterial cells in a population to regulate certain gene expression and phenotypic behaviours. This type of gene regulation is known as quorum sensing. Other names for these types of enzymes are Quorum-quenching N-acyl-homoserine lactonase, acyl homoserine degrading enzyme, acyl-homoserine lactone acylase, AHL lactonase, AHL-degrading enzyme, AHL-inactivating enzyme, AHLase, AhlD, AhlK, AiiA, AiiA lactonase, AiiA-like protein, AiiB, AiiC, AttM, delactonase, lactonase-like enzyme, N-acyl homoserine lactonase, N-acyl homoserine lactone hydrolase, N-acyl-homoserine lactone lactonase, N-acyl-L-homoserine lactone hydrolase, quorum-quenching lactonase, quorum-quenching N-acyl homoserine lactone hydrolase.

Enzyme mechanism Lactonase hydrolyzes the ester bond of the homoserine lactone ring of acylated homoserine lactones. In hydrolysing the lactone bond, lactonase prevents these signaling molecules from binding to their target transcriptional regulators, thus inhibiting quorum sensing.

Enzyme Structure A dinuclear zinc binding site is conserved in all known lactonases and essential for enzyme activity and protein folding. Zn1 is tetracoordinated by His104, His106, His169, and the bridging hydroxide ion. Zn2 has five ligands, including Asp191, His235, His109, Asp108, and the bridging hydroxide ion. The metal ions assist in polarizing the lactone bond, increasing the electrophilicity of the lactone ring’s carbonyl carbon. Isotopic labeling studies indicated that the ring opening occurs via an addition elimination reaction with water addition shown below.

Biological Function Lactonases are able to interfere with AHL-mediated quorum sensing. Some examples of these lactonases are AiiA produced by Bacillus species, AttM and AiiB produced by Agrobacterium tumefaciens, and QIcA produced by Hyphomicrobiales species. Lactonases have been reported for Bacillus, Agrobacterium, Rhodococcus, Streptomyces, Arthrobacter, Pseudomonas, and Klebsiella. The Bacillus cereus group (consisting of B. cereus, B. thuringiensis, B. mycoides, and B. anthracis) was found to contain nine genes homologous to the AiiA gene that encode AHL-inactivating enzymes, with the catalytic zinc-binding motif conserved in all cases. In the phytopathogen A. tumefaciens, AiiB lactonase acts as a fine modulator that essentially delays the release of lactone OC8-HSL and the resultant number of tumors produced by the pathogen. AttM lactonase mediates the degradation of the lactone OC8-HSL in wounded plant tissues. The primary activity of the anti-atherosclerotic paraoxonase (PON) enzymes is as lactonase. Oxidized polyunsaturated fatty acids (notably in oxidized low-density lipoprotein) form lactone-like structures that are PON substrates.

Ecology It is still unclear the ecological effects of lactonase but it has been proposed that since bacteria mostly coexist with other microorganisms in the environment, some bacteria strains could have evolved its feeding strategies and utilize AHLs as their main resource for energy and nitrogen.

Applications Understanding the mechanisms and purposes of lactonase activity could lead to potential applied roles for these lactonases to control bacterial infections by inhibiting quorum-sensing activity and bring about profound effects on human health and the environment. However, in both the chemical and enzymatic lactonolysis, the reaction is reversible, complicating direct therapeutic application of lactonases. Pseudomonas aeruginosa, is an AHL-producing bacteria an opportunistic pathogen that infects immuno-compromised patients, and is found in lung infections of cystic fibrosis patients. P. aeruginosa relies on quorum sensing via production of lactones N-butanoyl-L-homoserine (C4-HSL) and N-(3-oxododecanoyl)-l-HSL (3-oxo-C12-HSL) to regulate swarming, toxin and protease production, and proper biofilm formation. The absence of one or more components of the quorum-sensing system results in a significant reduction in virulence of the pathogen. Erwinia carotovora is a plant pathogen that causes soft rot in a number of crops such as potatoes and carrots by using N-hexanoyl-l-HSL (C6-HSL) quorum sensing to evade the plant's defense systems and coordinate its production of pectate lyase during the infection process. Plants expressing AHL-Lactonase were shown to demonstrate enhanced resistance to infection from the pathogen Erwinia carotovora. Expression of virulence genes in E. Carotovora is regulated by N-(3-oxohexanoyl)-L-homoserine lactone (OHHL). Presumably, OHHL-hydrolysis via lactonase reduced OHHL levels, inhibiting the quorum-sensing systems driving virulence gene expression.

See also 1,4-lactonase 2-pyrone-4,6-dicarboxylate lactonase 3-oxoadipate enol-lactonase Actinomycin lactonase Deoxylimonate A-ring-lactonase Gluconolactonase L-rhamnono-1,4-lactonase Limonin-D-ring-lactonase Steroid-lactonase Triacetate-lactonase Xylono-1,4-lactonase

References

Illustrations

Worked examples

Example 1 — a first encounter with Lactonase

Start with the simplest possible case. Write down what Lactonase claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, 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 Lactonase 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 Lactonase 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 Lactonase

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

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

Frequently asked questions

What is Lactonase in simple terms?

Why does Lactonase matter?

Because it connects several chemistry 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 Lactonase?

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 Lactonase.