RESEARCH: VIOLAXANTHIN-DEEPOXIDASE-STRUCTURE
FOLDING PROJECT #19334 PROFILE

Plants change how they use sunlight based on the light levels. A process called the xanthophyll cycle helps protect plants from too much light. This involves changing a pigment called violaxanthin into zeaxanthin, which acts like a sunscreen and protects against damage. Scientists studied an enzyme called VDE that's key to this process. They found that VDE changes shape depending on the acidity of the plant cells, allowing it to work better under bright light.

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.

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 (glucose). This process releases oxygen as a byproduct. It's essential for life on Earth as it provides the oxygen we breathe and the base of the food chain.

violaxanthin

A yellow carotenoid pigment found in plants.

Violaxanthin is a type of pigment found in plants that helps protect them from excess light. It's part of the xanthophyll cycle, which allows plants to adjust their photosynthetic activity based on light intensity.

zeaxanthin

A yellow carotenoid pigment found in plants.

Zeaxanthin is another type of pigment found in plants. It's also part of the xanthophyll cycle and helps protect plants from excess light damage. Plants convert violaxanthin to zeaxanthin when exposed to strong light.

thylakoid

A membrane-bound compartment within chloroplasts where photosynthesis takes place.

Thylakoids are small, flattened sacs inside plant cells' chloroplasts. They contain chlorophyll and other pigments involved in capturing light energy for photosynthesis. The thylakoid membranes also hold the enzymes that drive the chemical reactions of photosynthesis.

violaxanthin deepoxidase (VDE)

Violaxanthin deepoxidase. An enzyme involved in the xanthophyll cycle.

VDE is an enzyme that plays a crucial role in the xanthophyll cycle, which helps plants regulate light absorption and protect themselves from excess light damage. It converts violaxanthin to zeaxanthin when light levels are high.

ascorbate

Another name for Vitamin C.

Ascorbate is a powerful antioxidant found in many plants and animals. It helps protect cells from damage caused by free radicals and plays a role in various metabolic processes.