RESEARCH: VIOLAXANTHIN-DEEPOXIDASE-STRUCTURE
FOLDING PROJECT #19331 PROFILE

Plants adjust their photosynthesis based on light. A process called the xanthophyll cycle uses a pigment called zeaxanthin to protect plants from excess light. An enzyme called VDE creates zeaxanthin when light is strong. VDE changes shape and becomes active in acidic environments. This allows it to efficiently break down harmful energy produced by light.

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 used by plants and some other organisms to convert sunlight, water, and carbon dioxide into glucose (sugar) for energy. This process releases oxygen as a byproduct.

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Xanthophyll Cycle

A series of biochemical reactions involving carotenoid pigments that protect plants from excess light energy.

The xanthophyll cycle helps plants manage excess sunlight by converting carotenoids like violaxanthin into zeaxanthin. This process dissipates excess energy as heat and protects against damaging reactive oxygen species.

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Violaxanthin

A type of carotenoid pigment involved in the xanthophyll cycle.

Violaxanthin is a yellow pigment found in plants that plays a crucial role in protecting them from harmful light. It converts to zeaxanthin during intense sunlight, dissipating excess energy as heat.

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Zeaxanthin

A type of carotenoid pigment involved in the xanthophyll cycle.

Zeaxanthin is a red-orange pigment produced by plants when exposed to intense sunlight. It helps protect them from damage by dissipating excess light energy as heat.

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Violaxanthin Deepoxidase (VDE)

violaxanthin deepoxidase

VDE is an enzyme crucial for converting violaxanthin into zeaxanthin during the xanthophyll cycle. This process helps plants regulate light energy and protect themselves from damage.

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Thylakoid Lumen

The internal space enclosed by the thylakoid membranes within chloroplasts.

The thylakoid lumen is a crucial compartment within plant chloroplasts where light-dependent reactions of photosynthesis take place. It's also where VDE enzyme functions.

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Ascorbate

The reduced form of vitamin C, an important antioxidant in plants.

Ascorbate is a vital molecule involved in plant metabolism and redox reactions. It acts as an antioxidant, protecting cells from damage by reactive oxygen species.

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Lipocalin

A family of proteins that bind and transport small hydrophobic molecules.

Lipocalins are a diverse group of proteins found in various organisms. They have a characteristic barrel-shaped structure that allows them to bind and transport small molecules like lipids, steroids, and odorants.