CHST5

CHST5

The structure of the CHST5 protein.

CHST5 (Carbohydrate Sulfotransferase 5) is an enzyme that plays a crucial role in the sulfation of carbohydrates. It is encoded by the CHST5 gene, which is located on chromosome 16 in humans. This gene is primarily expressed in the cornea, where it is responsible for the sulfation of keratan sulfate (KS) chains.

Structure and Function

The CHST5 protein consists of 396 amino acids and belongs to the sulfotransferase family. It contains a conserved sulfotransferase domain, which is responsible for the transfer of sulfate groups from a donor molecule to a target carbohydrate. In the case of CHST5, the target carbohydrate is keratan sulfate.

Keratan sulfate is a glycosaminoglycan (GAG) that is found in various tissues, including the cornea, cartilage, and brain. Sulfation of keratan sulfate is essential for its proper function, as it affects its interactions with other molecules and proteins. CHST5 specifically sulfates the galactose residues of keratan sulfate, leading to the formation of sulfated keratan sulfate chains.

Role in Corneal Transparency

The cornea is the transparent outer layer of the eye that plays a crucial role in focusing light onto the retina. The transparency of the cornea is essential for clear vision. The sulfation of keratan sulfate by CHST5 is critical for maintaining corneal transparency.

Sulfated keratan sulfate chains in the cornea interact with collagen fibrils, providing structural stability and maintaining the regular arrangement of collagen fibers. These interactions contribute to the transparency of the cornea by preventing light scattering and maintaining a clear optical pathway.

Mutations in the CHST5 gene can lead to a condition known as macular corneal dystrophy (MCD). MCD is characterized by the accumulation of unsulfated keratan sulfate in the cornea, leading to corneal clouding and vision impairment. This condition highlights the importance of CHST5 in maintaining corneal transparency.

Clinical Significance

Mutations in the CHST5 gene have been associated with various forms of macular corneal dystrophy, including types I, II, and III. These mutations can result in reduced or absent CHST5 activity, leading to the accumulation of unsulfated keratan sulfate in the cornea.

Diagnosis of macular corneal dystrophy typically involves a thorough clinical examination, including corneal imaging and genetic testing. Treatment options for this condition are limited, and management often focuses on symptomatic relief, such as the use of contact lenses or corneal transplantation in severe cases.

See Also

• Glycosaminoglycan
• Cornea
• Macular corneal dystrophy
• Sulfotransferase
• Keratan sulfate