Defective cystathionine beta-synthase regulation by S-adenosylmethionine in a partially pyridoxine responsive homocystinuria patient.

Abstract

We determined the molecular basis of cystathionine beta-synthase (CBS) deficiency in a partially pyridoxine-responsive homocystinuria patient. Direct sequencing of the entire CBS cDNA revealed the presence of a homozygous G1330A transition. This mutation causes an amino acid change from aspartic acid to asparagine (D444N) in the regulatory domain of the protein and abolishes a TaqI restriction site at DNA level. Despite the homozygous mutation, CBS activities in extracts of cultured fibroblasts of this patient were not in the homozygous but in the heterozygous range. Furthermore, we observed no stimulation of CBS activity by S-adenosylmethionine, contrary to a threefold stimulation in control fibroblast extract. The mutation was introduced in an E. coli expression system and CBS activities were measured after addition of different S-adenosylmethionine concentrations (0-200 microM). Again, we observed a defective stimulation of CBS activity by S-adenosylmethionine in the mutated construct, whereas the normal construct showed a threefold stimulation in activity. These data suggest that this D444N mutation interferes in S-adenosylmethionine regulation of CBS. Furthermore, it indicates the importance of S-adenosylmethionine regulation of the transsulfuration pathway in homocysteine homeostasis in humans.

• Authors: L A Kluijtmans, G H Boers, E M Stevens, W O Renier, J P Kraus, F J Trijbels, L P van den Heuvel, H J Blom
• Journal: The Journal of clinical investigation (J Clin Invest) Vol. 98 Issue 2 Pg. 285-9 (Jul 15 1996) ISSN: 0021-9738 [Print] United States
• PMID: 8755636 (Publication Type: Case Reports, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• DNA Primers
• Aspartic Acid
• Asparagine
• S-Adenosylmethionine
• DNA
• Cystathionine beta-Synthase
• Pyridoxine

Topics

• Adult
• Amino Acid Sequence
• Asparagine
• Aspartic Acid
• Base Sequence
• Cystathionine beta-Synthase (deficiency, genetics, metabolism)
• DNA (blood)
• DNA Primers
• Female
• Gene Expression Regulation, Enzymologic (drug effects)
• Heterozygote
• Homocystinuria (enzymology, genetics)
• Homozygote
• Humans
• Male
• Molecular Sequence Data
• Pedigree
• Point Mutation
• Polymerase Chain Reaction
• Pyridoxine (therapeutic use)
• Reference Values
• S-Adenosylmethionine (pharmacology)