RESEARCH: VIOLAXANTHIN-DEEPOXIDASE-STRUCTURE
FOLDING PROJECT #19337 PROFILE

Plants change how they make food (photosynthesis) based on light. When it's bright, they use a special process called the xanthophyll cycle to avoid damage from too much light. This involves an enzyme called VDE that changes shape depending on the acidity of the plant cell. Scientists studied VDE and found that it works best when acidic, allowing it to break down a molecule called violaxanthin into zeaxanthin, which helps protect plants from light damage.

Note: This TLDR is a simplication and may not be 100% accurate.

To adapt to shifting lighting conditions, plants modify their photosynthetic activity.

The xanthophyll cycle, in which the carotenoid violaxanthin is transformed into zeaxanthin in strong light, plays a key role in controlling photosynthesis.

This process activates the disposal of excess absorbed energy as heat and the scavenging of reactive oxygen species.

When photosynthetic electron transport exceeds the capacity of assimilatory reactions, violaxanthin deepoxidase (VDE), the enzyme responsible for zeaxanthin synthesis, is activated by the acidification of the thylakoid lumen.

At neutral pH, VDE is a soluble and inactive enzyme, but at acidic pH, it attaches to the thylakoid membrane where it binds its substrate.

Ascorbate is used by VDE as a cosubstrate as well, and its pH-dependent Km may indicate a preference for ascorbic acid.

At neutral and acidic pH, we established the structures of the central lipocalin domain of VDE (VDEcd).

VDEcd is monomeric and has its active site blocked by a lipocalin barrel at neutral pH.

The barrel unwinds and the enzyme emerges as a dimer during acidification.

The two violaxanthin beta-ionone rings may be deep oxidized simultaneously in two channels that connect the two active sites of the dimer, giving VDE an ideal example of an asymmetric enzyme's adaptation to its symmetric substrate.

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Photosynthesis

The process by which plants convert light energy into chemical energy.

Photosynthesis is the vital process that allows plants to use sunlight, water, and carbon dioxide to create their own food (sugars). This process takes place in chloroplasts within plant cells and releases oxygen as a byproduct.

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Xanthophyll Cycle

A pigment cycle in plants that regulates light absorption and protects against photodamage.

The xanthophyll cycle involves the conversion of carotenoids like violaxanthin to zeaxanthin in response to high light conditions. This helps plants dissipate excess energy as heat and prevent damage from reactive oxygen species.

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Violaxanthin

A carotenoid pigment involved in the xanthophyll cycle.

Violaxanthin is a type of carotenoid pigment found in plants that plays a role in light harvesting and protecting against photodamage. It converts to zeaxanthin under high light conditions.

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Zeaxanthin

A carotenoid pigment involved in the xanthophyll cycle.

Zeaxanthin is a type of carotenoid pigment that accumulates in plants under high light conditions. It helps protect against photodamage by dissipating excess energy as heat.

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Violaxanthin Deepoxidase (VDE)

An enzyme that catalyzes the conversion of violaxanthin to zeaxanthin.

Violaxanthin deepoxidase (VDE) is an enzyme essential for plant adaptation to light. It converts violaxanthin into zeaxanthin in response to high light conditions, facilitating the xanthophyll cycle and protecting plants from photodamage.

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Thylakoid Lumen

The space inside the thylakoid membrane of a chloroplast.

The thylakoid lumen is a compartment within plant chloroplasts where photosynthesis takes place. It contains enzymes and proteins involved in electron transport and energy conversion.

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Ascorbate

A water-soluble antioxidant also known as vitamin C.

Ascorbate (vitamin C) is a crucial antioxidant that protects cells from damage caused by reactive oxygen species. It plays various roles in plant metabolism, including photosynthesis and stress response.