ATP-dependent degradation of a mutant serine: pyruvate/alanine:glyoxylate aminotransferase in a primary hyperoxaluria type 1 case.

Abstract

Primary hyperoxaluria type 1 (PH 1), an inborn error of glyoxylate metabolism characterized by excessive synthesis of oxalate and glycolate, is caused by a defect in serine:pyruvate/alanine:glyoxylate aminotransferase (SPT/AGT). This enzyme is peroxisomal in human liver. Recently, we cloned SPT/AGT-cDNA from a PH 1 case, and demonstrated a point mutation of T to C in the coding region of the SPT/AGT gene encoding a Ser to Pro substitution at residue 205 (Nishiyama, K., T. Funai, R. Katafuchi, F. Hattori, K. Onoyama, and A. Ichiyama. 1991. Biochem. Biophys. Res. Commun. 176:1093-1099). In the liver of this patient, SPT/AGT was very low with respect to not only activity but also protein detectable on Western blot and immunoprecipitation analyses. Immunocytochemically detectable SPT/AGT labeling was also low, although it was detected predominantly in peroxisomes. On the other hand, the level of translatable SPT/AGT-mRNA was higher than normal, indicating that SPT/AGT had been synthesized in the patient's liver at least as effectively as in normal liver. Rapid degradation of the mutant SPT/AGT was then demonstrated in transfected COS cells and transformed Escherichia coli, accounting for the low level of immunodetectable mutant SPT/AGT in the patient's liver. The mutant SPT/AGT was also degraded much faster than normal in an in vitro system with a rabbit reticulocyte extract, and the degradation in vitro was ATP dependent. These results indicate that a single amino acid substitution in SPT/AGT found in the PH1 case leads to a reduced half-life of this protein. It appears that the mutant SPT/AGT is recognized in cells as an abnormal protein to be eliminated by degradation.

• Authors: K Nishiyama, T Funai, S Yokota, A Ichiyama
• Journal: The Journal of cell biology (J Cell Biol) Vol. 123 Issue 5 Pg. 1237-48 (Dec 1993) ISSN: 0021-9525 [Print] United States
• PMID: 8245128 (Publication Type: Case Reports, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Recombinant Proteins
• Adenosine Triphosphate
• Transaminases
• Alanine Transaminase
• Alanine-glyoxylate transaminase
• serine-pyruvate aminotransferase

Topics

• Adenosine Triphosphate (pharmacology)
• Alanine Transaminase (genetics, metabolism)
• Blotting, Northern
• Blotting, Western
• Cell-Free System
• Cells, Cultured
• Cytoplasm (metabolism)
• Humans
• Hyperoxaluria, Primary (enzymology, genetics)
• Immunohistochemistry
• Liver (enzymology, ultrastructure)
• Microbodies (metabolism)
• Middle Aged
• Mitochondria (metabolism)
• Point Mutation
• Precipitin Tests
• Protein Biosynthesis
• Recombinant Proteins (drug effects, metabolism)
• Transaminases (genetics, metabolism)
• Transformation, Genetic