W474C amino acid substitution affects early processing of the alpha-subunit of beta-hexosaminidase A and is associated with subacute G(M2) gangliosidosis.

Abstract

Mutations in the HEXA gene, encoding the alpha-subunit of beta-hexosaminidase A (Hex A), that abolish Hex A enzyme activity cause Tay-Sachs disease (TSD), the fatal infantile form of G(M2) gangliosidosis, Type 1. Less severe, subacute (juvenile-onset) and chronic (adult-onset) variants are characterized by a broad spectrum of clinical manifestations and are associated with residual levels of Hex A enzyme activity. We identified a 1422 G-->C (amino acid W474C) substitution in the first position of exon 13 of HEXA of a non-Jewish proband who manifested a subacute variant of G(M2) gangliosidosis. On the second maternally inherited allele, we identified the common infantile disease-causing 4-bp insertion, +TATC 1278, in exon 11. Pulse-chase analysis using proband fibroblasts revealed that the W474C-containing alpha-subunit precursor was normally synthesized, but not phosphorylated or secreted, and the mature lysosomal alpha-subunit was not detected. When the W474C-containing alpha-subunit was transiently co-expressed with the beta-subunit to produce Hex A (alphabeta) in COS-7 cells, the mature alpha-subunit was present, but its level was much lower than that from normal alpha-subunit transfections, although higher than in those cells transfected with an alpha-subunit associated with infantile TSD. Furthermore, the precursor level of the W474C alpha-subunit was found to accumulate in comparison to the normal alpha-subunit precursor levels. We conclude that the 1422 G-->C mutation is the cause of Hex A enzyme deficiency in the proband. The resulting W474C substitution clearly interferes with alpha-subunit processing, but because the base substitution falls at the first position of exon 13, aberrant splicing may also contribute to Hex A deficiency in this proband.

• Authors: E Petroulakis, Z Cao, J T Clarke, D J Mahuran, G Lee, B Triggs-Raine
• Journal: Human mutation (Hum Mutat) Vol. 11 Issue 6 Pg. 432-42 ( 1998) ISSN: 1059-7794 [Print] United States
• PMID: 9603435 (Publication Type: Case Reports, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Hexosaminidase A
• beta-N-Acetylhexosaminidases

Topics

• Adolescent
• Age of Onset
• Amino Acid Sequence
• Amino Acid Substitution
• Animals
• COS Cells
• Cell Line
• Electrophoresis, Gel, Pulsed-Field
• Exons
• Fibroblasts (enzymology)
• Hexosaminidase A
• Humans
• Male
• Molecular Sequence Data
• Mutation
• Phosphorylation
• Protein Processing, Post-Translational
• Sequence Homology, Amino Acid
• Tay-Sachs Disease (enzymology, genetics)
• Transfection
• beta-N-Acetylhexosaminidases (chemistry, genetics, metabolism)