RESEARCH: PHOTOSYNTHESIS
FOLDING PROJECT #19329 PROFILE

Plants change how they photosynthesize in different light. A process called the xanthophyll cycle helps them deal with too much sunlight by turning a pigment, violaxanthin, into zeaxanthin. This protects plants from damage. The project relates to how an enzyme called VDE, which makes zeaxanthin, changes shape depending on the acidity of plant cells to work better.

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 (sugar). This process releases oxygen as a byproduct and is essential for life on Earth.

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xanthophyll cycle

A biochemical pathway that regulates light absorption in plants.

The xanthophyll cycle involves changes in carotenoid pigments like violaxanthin and zeaxanthin. When light is strong, these pigments help protect plants from damage by dissipating excess energy as heat.

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violaxanthin

A type of carotenoid pigment found in plants.

Violaxanthin is a yellow pigment that helps plants absorb light energy during photosynthesis. It can be converted to zeaxanthin when light conditions are intense.

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zeaxanthin

A type of carotenoid pigment found in plants.

Zeaxanthin is a red-orange pigment that helps protect plants from damage caused by excess light. It's produced when violaxanthin is converted during the xanthophyll cycle.

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violaxanthin deepoxidase (VDE)

Violaxanthin deepoxidase (VDE) - An enzyme that catalyzes the conversion of violaxanthin to zeaxanthin.

VDE is a crucial enzyme in the xanthophyll cycle. It's responsible for converting violaxanthin into zeaxanthin, which helps protect plants from excessive light.

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ascorbate

A reduced form of vitamin C.

Ascorbate is a powerful antioxidant that plays various roles in plant metabolism, including supporting photosynthesis and protecting cells from damage.

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thylakoid lumen

The internal space enclosed by the thylakoid membranes in chloroplasts.

The thylakoid lumen is a compartment within chloroplasts where light-dependent reactions of photosynthesis occur. It's important for maintaining pH gradients that drive energy production.

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lipocalin domain

A common protein structural motif found in various proteins.

Lipocalin domains are small protein folds that often bind to small hydrophobic molecules. They play roles in diverse biological processes, including transport and signal transduction.