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cystathionine beta-synthase (serine sulfhydrase, beta-thionase, CBS)
Function:
- vitamin B6-dependent enzyme catalyzing the condensation of cysteine with serine to form cystathionine
- allosterically activated by adenosylmethionine (AdoMet)
- amino-acid biosynthesis; L-cysteine biosynthesis
- L-cysteine from L-homocysteine & L-serine: step 1/2
L-serine + L-homocysteine L-cystathionine + H2O
Cofactor: pyridoxal phosphate
Structure:
- homotetramer
- belongs to the cysteine synthase/cystathionine beta-synthase family
- contains 1 CBS domain
Compartment: cytoplasm, nucleus
Alternative splicing: named isoforms=2
Expression:
- in adults, expressed in liver & pancreas > heart & brain > lung & kidney.
- in fetus, expressed in brain, liver & kidney
Pathology:
- homozoygous defects in CBS are associated with homocystinuria
- heterozygous deficiency is prevalent in the US with a frequency of 1 in 300
- hyperhomocysteinemia results from heterozygous deficiency
Laboratory:
- CBS gene mutation
- cystathionine beta-synthase in fibroblasts
Interactions
molecular events
Related
cystathionine
homocystinuria
hyperhomocysteinemia
methionine metabolism (trans-sulfuration pathway)
pyridoxal phosphate
General
hydro-lyase, hydratase or dehydratase
Properties
SIZE: entity length = 551 aa
MW = 61 kD
COMPARTMENT: cytoplasm
cell nucleus
MOTIF: Iron [Fe]-binding site
SITE: 52-52
Iron [Fe]-binding site
SITE: 65-65
cofactor-binding site [119-119]
FOR-BINDING-OF: pyridoxal phosphate
cofactor-binding site [149-149]
FOR-BINDING-OF: pyridoxal phosphate
Pyridoxal phosphate binding {256-260}
cofactor-binding site [349-349]
COFACTOR-BOUND: pyridoxal phosphate
BOUND-VIA: lysine residue
CBS {416-469}
Database Correlations
OMIM correlations
UniProt P35520
PFAM correlations
Kegg hsa:875
ENZYME 4.2.1.22
References
- Stryer Biochemistry WH Freeman & Co, New York,1988,
pg 583-84
- Harrison's Principles of Internal Medicine, 14th ed.
Fauci et al (eds), McGraw-Hill Inc. NY, 1998, pg 2199
- CBS mutation database
http://www.uchsc.edu/cbs/cbsdata/cgidata.htm
- GeneReviews
https://www.genecards.org/cgi-bin/carddisp.pl?gene=CBS
- UniProt :accession P35520