biology

Plasma membrane H+-ATPase

Plasma membrane H+-ATPase 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 Plasma membrane H+-ATPase rather than just read about it. In short: The P-type plasma membrane H+-ATPase is found in plants and fungi. For the gastric H+/K+ ATPase (involved in the acidification of the stomach in mammals), see Hydrogen potassium ATPase.

Key takeaways

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Reference excerpt

The P-type plasma membrane H+-ATPase is found in plants and fungi. For the gastric H+/K+ ATPase (involved in the acidification of the stomach in mammals), see Hydrogen potassium ATPase.

Plasma membrane H+-ATPase (P-type) This enzyme belongs to the family of hydrolases, specifically those acting on acid anhydrides to catalyse transmembrane movement of substances. To be specific, the protein is a part of the P-type ATPase family. The systematic name of this enzyme class is ATP phosphohydrolase (H+-exporting). H+-exporting ATPase is also known as proton ATPase or more simply proton pump. Other names in common use include proton-translocating ATPase, yeast plasma membrane H+-ATPase, plant plasma membrane H+-ATPase, yeast plasma membrane ATPase, plant plasma membrane ATPase, and ATP phosphohydrolase. The yeast (Saccharomyces cerevisiae) enzyme is encoded by the gene Pma1 and hence referred to as Pma1p.

Function and location The plasma membrane H+-ATPase or proton pump creates the electrochemical gradients in the plasma membrane of plants, fungi, protists, and many prokaryotes. Here, proton gradients are used to drive secondary transport processes. As such, it is essential for the uptake of most metabolites, and also for plant responses to the environment (e.g., movement of leaves). Plasma membrane H+-ATPases are specific for plants, fungi, and protists; and Na+/K+-ATPases are specific for animal cells. These two groups of P-type ATPases, although not from the same subfamily, seem to perform a complementary function in plants/fungi/protists and animal cells, namely the creation of an electrochemical gradient used as an energy source for secondary transport.

Structural studies

Structural information on P-type plasma membrane (PM) proton ATPases are scarce compared to that obtained for SERCA1a. A low resolution structure from 2D crystals of the PM H+-ATPase from Neurospora crassa is, as of medio 2011, the only structural information on the fungal H+-ATPase. For the plant counterpart, a crystal structure of the AHA2 PM H+-ATPase from Arabidopsis thaliana has been obtained from 3D crystals with a resolution of 3.6 Å. The structure of AHA2 clearly identifies three cytosolic domains corresponding to the N (nucleotide binding), P (phosphorylation), and A (actuator) domains, similar to those observed in the SR Ca2+-ATPase and also verifies the presence of ten transmembrane helices. The 3D crystal structure shows the AHA2 PM H+-ATPase in a so-called quasi-occluded E1 state with the non-hydrolysable ATP analogue AMPPCP bound, and the overall fold of the catalytic unit reveals a high degree of structural similarity to the SR Ca2+-ATPase and the Na+,K+-ATPase. The overall arrangement of the domains is similar to that observed for the occluded E1 conformation of the SR Ca2+-ATPase, and based on comparison with structural data for the other conformations of the SR Ca2+-ATPase, it was suggested that the structure of the AHA2 PM H+-ATPase represents a novel E1 intermediate. A distinct feature of the PM H+-ATPase not observed in other P-type ATPases is the presence of a large cavity in the transmembrane domain formed by M4, M5 and M6.

Regulation Precise regulation of PM H+-ATPase activity is crucial to the plant. Over-expression of the PM H+-ATPase is compensated by a down-regulation of activity, whereas deletion of an isoform is compensated by redundancy as well as augmented activity of other isoforms by increased level of post-translational modifications. The PM H+-ATPase is subject to autoinhibition, which negatively regulates the activity of the pump and keeps the enzyme in a low activity state where ATP hydrolytic activity is partly uncoupled from ATP hydrolysis,. Release from the autoinhibitory restraints requires posttranslational modifications such as phosphorylation and interacting proteins. Autoinhibition is achieved by the N- and C-termini of the protein - communication between the two termini facilitates the necessary precise control of pump activity. The autoinhibitory C-terminal domain can be displaced by phosphorylation of the penultimate Thr residue and the subsequent binding of 14-3-3 proteins. The PM H+-ATPase is the first P-type ATPase for which both termini have been demonstrated to take part in the regulation of protein activity.

Physiological roles in plants Plasma membrane H+-ATPases are found throughout the plant in all cell types investigated, but some cell types have much higher concentrations of H+-ATPase than others. In general, these cell types are specialised for intensive active transport and accumulate solutes from their surroundings. Most studies of these roles come from genetic studies on Arabidopsis thaliana. H+-ATPases in plants are expressed from a multigene subfamily, and Arabidopsis thaliana for instance, have 12 different H+-ATPase genes. Some important physiological processes the plant H+-ATPase is involved in are:

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Worked examples

Example 1 — a first encounter with Plasma membrane H+-ATPase

Start with the simplest possible case. Write down what Plasma membrane H+-ATPase 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 Plasma membrane H+-ATPase 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 Plasma membrane H+-ATPase 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 Plasma membrane H+-ATPase

In research: Plasma membrane H+-ATPase 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 Plasma membrane H+-ATPase 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: Plasma membrane H+-ATPase is common in secondary-school and first-year university syllabi. It links to neighbouring topics EC 3.6.3, Enzymes of known structure, Transmembrane proteins, so understanding it makes those chapters shorter.
In everyday life: Look for Plasma membrane H+-ATPase 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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Frequently asked questions

What is Plasma membrane H+-ATPase in simple terms?

The P-type plasma membrane H+-ATPase is found in plants and fungi. For the gastric H+/K+ ATPase (involved in the acidification of the stomach in mammals), see Hydrogen potassium ATPase.

Why does Plasma membrane H+-ATPase 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 Plasma membrane H+-ATPase?

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 Plasma membrane H+-ATPase.