RESEARCH: VIOLAXANTHIN-DEPOXIDASE-STRUCTURE
FOLDING PROJECT #19330 PROFILE

Plants change how they make food based on sunlight. When it's bright, they use a process called the xanthophyll cycle to protect themselves from excess light energy. This involves converting violaxanthin into zeaxanthin, which helps dissipate heat and prevent damage. Scientists studied an enzyme called VDE that plays a key role in this process. They found that VDE changes shape when exposed to acidic conditions, allowing it to efficiently convert violaxanthin into zeaxanthin.

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 how plants use sunlight, water, and carbon dioxide to make their own food (glucose). This process releases oxygen as a byproduct. It's essential for life on Earth because it provides the oxygen we breathe and the basis of most food chains.

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carotenoid

A class of organic pigments found in plants and some other organisms.

Carotenoids are colorful pigments that give fruits and vegetables their vibrant hues. They play a role in photosynthesis by absorbing light energy and protecting plants from damage caused by excess sunlight.

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violaxanthin

A type of carotenoid pigment involved in the xanthophyll cycle.

Violaxanthin is a carotenoid that helps plants protect themselves from damage caused by excess light. It's part of the xanthophyll cycle, which involves the conversion between different carotenoids to regulate photosynthesis.

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zeaxanthin

A type of carotenoid pigment involved in the xanthophyll cycle.

Zeaxanthin is a carotenoid that helps plants dissipate excess light energy as heat. It's produced when violaxanthin is converted during the xanthophyll cycle.

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violaxanthin deepoxidase (VDE)

Violaxanthin deepoxidase

VDE is an enzyme that plays a crucial role in the xanthophyll cycle. It converts violaxanthin into zeaxanthin in response to high light conditions.

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ascorbate

The ionized form of vitamin C.

Ascorbate is a powerful antioxidant that helps protect cells from damage caused by free radicals. It's also involved in various metabolic processes and plays a role as a cofactor for some enzymes.

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thylakoid lumen

The space inside the thylakoid membranes of chloroplasts.

The thylakoid lumen is where light-dependent reactions of photosynthesis occur. It's a specialized compartment within chloroplasts that helps regulate pH and concentration gradients essential for energy production.