Cystathionine beta synthase

CBSsequence

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Cysteine biosynthesis.svg

Enzyme involved in the metabolism of homocysteine

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Identifiers
EC number	4.2.1.22
CAS number	9026-88-4
Alt. names
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway

Cystathionine beta synthase (CBS) is an enzyme that plays a crucial role in the metabolism of the amino acid homocysteine. It catalyzes the first step of the transsulfuration pathway, converting homocysteine to cystathionine. This reaction is pyridoxal phosphate (PLP)-dependent and involves the condensation of homocysteine with serine.

Function

CBS is a key enzyme in the methionine cycle, which is essential for the regulation of homocysteine levels in the body. Elevated levels of homocysteine, a condition known as hyperhomocysteinemia, are associated with an increased risk of cardiovascular disease, stroke, and other health issues. By converting homocysteine to cystathionine, CBS helps to maintain homocysteine at safe levels.

Structure

CBS is a homotetramer, meaning it consists of four identical subunits. Each subunit contains a PLP-binding domain, which is essential for its enzymatic activity. The enzyme also has a heme-binding domain, which is thought to play a regulatory role.

Genetic Aspects

The gene encoding CBS is located on chromosome 21 in humans. Mutations in the CBS gene can lead to homocystinuria, a rare genetic disorder characterized by high levels of homocysteine in the blood and urine. This condition can result in a variety of symptoms, including developmental delay, osteoporosis, and thromboembolism.

Clinical Significance

Deficiencies in CBS activity can lead to elevated homocysteine levels, which are a risk factor for several diseases. Homocystinuria is the most well-known condition associated with CBS deficiency. Treatment often involves dietary management and supplementation with vitamin B6, vitamin B12, and folate to help reduce homocysteine levels.

Research

Ongoing research is focused on understanding the detailed mechanisms of CBS function and regulation, as well as developing new treatments for conditions associated with CBS deficiency. Studies are also exploring the broader implications of homocysteine metabolism in health and disease.

See also

• Homocysteine
• Methionine
• Transsulfuration pathway
• Homocystinuria
• Pyridoxal phosphate