biology

Photoactive yellow protein

Photoactive yellow protein 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 Photoactive yellow protein rather than just read about it. In short: In molecular biology, the PYP domain (photoactive yellow protein) is a p-coumaric acid-binding protein domain. They are present in various proteins in bacteria.

Key takeaways

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

Reference excerpt

In molecular biology, the PYP domain (photoactive yellow protein) is a p-coumaric acid-binding protein domain. They are present in various proteins in bacteria. PYP is a highly soluble globular protein with an alpha/beta fold structure. It is a member of the PAS domain superfamily, which also contains a variety of other kinds of photosensory proteins. PYP was first discovered in 1985. A recently (2016) developed chemogenetic system named FAST (Fluorescence-Activating and absorption Shifting Tag) was engineered from PYP to specifically and reversibly bind a series of hydroxybenzylidene rhodanine (HBR) derivatives for their fluorogenic properties. Upon interaction with FAST, the fluorogen is locked into a fluorescent conformation unlike when in solution. This new protein labelling system is used in a variety of microscopy and cytometry setups.

p-Coumaric acid p-Coumaric acid is a cofactor of PYP. Adducts of p-coumaric acid bound to PYP form crystals that diffract well for x-ray crystallography experiments. These structural studies have provided insight into photosensitive proteins, e.g. the role of hydrogen bonding, molecular isomerization and photoactivity.

Photochemical transitions It was originally believed that due to light emissions resembling that of retinal bound rhodopsin, the photosensor molecule bound to PYP should resemble the structure of retinal bound rhodopsin, the photosensor molecule bound to PYP should resemble the structure of retinal. Scientists were therefore amazed when the PYP Cys 69 was bound by a thiol ester linkage to the light sensitive prosthetic group p-coumaric acid. During the photoreactive mechanism:

Light absorption yields the native protein to absorb a maximum wavelength of 446 nm, ε = 45500 M−1 cm−1. Within a nanosecond the absorbed maximum wavelength is shifted to 465 nm. Then on a sub-millisecond timescale is excited to a 355 nm state.

These observed phenomena are due to the trans–cis isomerization of the vinyl trans double bond in the p-coumaric acid. Scientists noted by observing the crystal structure of p-coumaric acid bound by PYP that the hydroxyl group connected to the C4 carbon of the phenyl ring appeared to be deprotonated – effectively a phenolate functional group. This was due to abnormally short hydrogen bonding lengths observed in the protein crystal structure.

Role of hydrogen bonding Hydrogen bonds in proteins such as PYP take part in interrelated networks, where at the center of p-coumaric acid's phenolate O4 atom, there is an oxyanion hole that is crucial for photosensory function. Oxyanion holes exist in enzymes to stabilize transitions states of reaction intermediates, thus stabilizing the trans–cis isomerization of p-coumaric acid. During the transition state it is believed that the p-coumaric acid phenolate O4 takes part in a hydrogen bond network between Glu46, Tyr42 and Thr50 of PYP. These interactions are apart from the thiol ester linkage to Cys 69 keeping p-coumaric acid in the ligand binding site. Upon transitioning to the cis-isomeric form of p-coumaric acid the favorable hydrogen bonds are no longer in close interaction.

References

Worked examples

Example 1 — a first encounter with Photoactive yellow protein

Start with the simplest possible case. Write down what Photoactive yellow protein 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 Photoactive yellow protein 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 Photoactive yellow protein 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 Photoactive yellow protein

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

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

Frequently asked questions

What is Photoactive yellow protein in simple terms?

In molecular biology, the PYP domain (photoactive yellow protein) is a p-coumaric acid-binding protein domain. They are present in various proteins in bacteria.

Why does Photoactive yellow protein 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 Photoactive yellow protein?

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 Photoactive yellow protein.