RESEARCH: PHOTOSYNTHESIS-REGULATION
FOLDING PROJECT #19336 PROFILE

Plants adjust photosynthesis based on light. A process called the xanthophyll cycle changes a pigment (violaxanthin) to zeaxanthin in bright light, helping plants get rid of excess energy and prevent damage. The enzyme VDE plays a key role, changing shape and becoming active in acidic conditions to make this happen.

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 create their own food (sugars) and release oxygen. It's a vital process for life on Earth as it provides the oxygen we breathe and forms the basis of most food chains.

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Xanthophyll Cycle

A series of biochemical reactions that involves the conversion of carotenoids, specifically violaxanthin to zeaxanthin.

The xanthophyll cycle is a plant's way of protecting itself from damage caused by excess light. When light is intense, plants convert violaxanthin to zeaxanthin, which helps dissipate excess energy as heat and protects against harmful reactive oxygen species.

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Violaxanthin

A type of carotenoid pigment found in plants.

Violaxanthin is a yellow-orange pigment that plays a key role in the xanthophyll cycle. It absorbs excess light energy and helps protect plants from damage.

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Zeaxanthin

A type of carotenoid pigment found in plants.

Zeaxanthin is a red-orange pigment that plays a key role in the xanthophyll cycle. It absorbs excess light energy and helps protect plants from damage.

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Violaxanthin Deepoxidase (VDE)

An enzyme responsible for the conversion of violaxanthin to zeaxanthin.

Violaxanthin deepoxidase (VDE) is a key enzyme in the xanthophyll cycle. It converts violaxanthin to zeaxanthin when plants are exposed to high light intensity, helping them protect themselves from damage.

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Ascorbate

The oxidized form of vitamin C.

Ascorbate is a powerful antioxidant that helps protect cells from damage caused by reactive oxygen species. Plants use ascorbate in various metabolic processes and to maintain their health.

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Lipocalin

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

Lipocalins are a diverse group of proteins found in various organisms. They have a characteristic structure with a central beta-barrel that binds to and transports small hydrophobic molecules.

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Thylakoid Lumen

The space inside the thylakoid membrane in chloroplasts.

The thylakoid lumen is a compartment within chloroplasts where light-dependent reactions of photosynthesis occur. It's important for maintaining a pH gradient that drives ATP synthesis.