Cystathionine gamma-synthase

Cystathionine gamma-synthase (CGS) is an essential enzyme involved in the biosynthesis of cysteine, an important amino acid in various biological processes. This article will provide an overview of CGS, its structure, function, and significance in human health.

Structure

CGS is a pyridoxal 5'-phosphate (PLP)-dependent enzyme encoded by the CBS gene. It consists of two identical subunits, each containing approximately 551 amino acids. The enzyme has a molecular weight of around 61 kDa. The crystal structure of CGS has been determined, revealing a homodimeric arrangement with each subunit consisting of three distinct domains: the N-terminal domain, the catalytic domain, and the C-terminal domain.

Function

The primary function of CGS is to catalyze the condensation of homocysteine and serine to form cystathionine. This reaction is a crucial step in the transsulfuration pathway, which converts homocysteine to cysteine. CGS plays a vital role in maintaining the balance of sulfur-containing amino acids in the body.

Significance in Human Health

Mutations in the CBS gene, which encodes CGS, can lead to a deficiency in CGS activity. This condition is known as homocystinuria, a rare inherited disorder characterized by elevated levels of homocysteine in the blood and urine. Homocystinuria can result in various health problems, including intellectual disability, skeletal abnormalities, cardiovascular complications, and eye abnormalities.

Role in Methionine Metabolism

CGS is also involved in the regulation of methionine metabolism. Methionine is an essential amino acid that serves as a precursor for various important molecules, including proteins, neurotransmitters, and DNA methylation. CGS helps maintain the balance between methionine and homocysteine levels, ensuring proper methionine utilization and preventing the accumulation of toxic metabolites.

See Also

• Cysteine
• Homocystinuria
• Transsulfuration pathway

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