Novel carboxypeptidase A6 (CPA6) mutations identified in patients with juvenile myoclonic and generalized epilepsy

Matthew R. Sapio, Monique Vessaz, Pierre Thomas, Pierre Genton, Lloyd D. Fricker, Annick Salzmann

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Carboxypeptidase A6 (CPA6) is a peptidase that removes C-terminal hydrophobic amino acids from peptides and proteins. The CPA6 gene is expressed in the brains of humans and animals, with high levels of expression during development. It is translated with a prodomain (as proCPA6), which is removed before secretion. The active form of CPA6 binds tightly to the extracellular matrix (ECM) where it is thought to function in the processing of peptides and proteins. Mutations in the CPA6 gene have been identified in patients with temporal lobe epilepsy and febrile seizures. In the present study, we screened for CPA6 mutations in patients with juvenile myoclonic epilepsy and identified two novel missense mutations: Arg36His and Asn271Ser. Patients harboring these mutations also presented with generalized epilepsy. Neither of the novel mutations was found in a control population. Asn271 is highly conserved in CPA6 and other related metallocarboxypeptidases. Arg36 is present in the prodomain and is not highly conserved. To assess structural consequences of the amino acid substitutions, both mutants were modeled within the predicted structure of the enzyme. To examine the effects of these mutations on enzyme expression and activity, we expressed the mutated enzymes in human embryonic kidney 293T cells. These analyses revealed that Asn271Ser abolished enzymatic activity, while Arg36His led to a ∼50% reduction in CPA6 levels in the ECM. Pulse-chase using radio-labeled amino acids was performed to follow secretion. Newly-synthesized CPA6 appeared in the ECM with peak levels between 2-8 hours. There was no major difference in time course between wild-type and mutant forms, although the amount of radiolabeled CPA6 in the ECM was lower for the mutants. Our experiments demonstrate that these mutations in CPA6 are deleterious and provide further evidence for the involvement of CPA6 mutations in the predisposition for several types of epilepsy.

Original languageEnglish (US)
Article numbere0123180
JournalPLoS One
Volume10
Issue number4
DOIs
StatePublished - Apr 13 2015

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Juvenile Myoclonic Epilepsy
Carboxypeptidases
carboxypeptidases
Generalized Epilepsy
epilepsy
mutation
Mutation
extracellular matrix
Extracellular Matrix
mutants
metallocarboxypeptidases
Enzymes
Amino Acids, Peptides, and Proteins
enzymes
Genes
secretion
peptides
Amino Acids
Febrile Seizures
missense mutation

ASJC Scopus subject areas

  • Agricultural and Biological Sciences(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Medicine(all)

Cite this

Novel carboxypeptidase A6 (CPA6) mutations identified in patients with juvenile myoclonic and generalized epilepsy. / Sapio, Matthew R.; Vessaz, Monique; Thomas, Pierre; Genton, Pierre; Fricker, Lloyd D.; Salzmann, Annick.

In: PLoS One, Vol. 10, No. 4, e0123180, 13.04.2015.

Research output: Contribution to journalArticle

Sapio, Matthew R. ; Vessaz, Monique ; Thomas, Pierre ; Genton, Pierre ; Fricker, Lloyd D. ; Salzmann, Annick. / Novel carboxypeptidase A6 (CPA6) mutations identified in patients with juvenile myoclonic and generalized epilepsy. In: PLoS One. 2015 ; Vol. 10, No. 4.
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abstract = "Carboxypeptidase A6 (CPA6) is a peptidase that removes C-terminal hydrophobic amino acids from peptides and proteins. The CPA6 gene is expressed in the brains of humans and animals, with high levels of expression during development. It is translated with a prodomain (as proCPA6), which is removed before secretion. The active form of CPA6 binds tightly to the extracellular matrix (ECM) where it is thought to function in the processing of peptides and proteins. Mutations in the CPA6 gene have been identified in patients with temporal lobe epilepsy and febrile seizures. In the present study, we screened for CPA6 mutations in patients with juvenile myoclonic epilepsy and identified two novel missense mutations: Arg36His and Asn271Ser. Patients harboring these mutations also presented with generalized epilepsy. Neither of the novel mutations was found in a control population. Asn271 is highly conserved in CPA6 and other related metallocarboxypeptidases. Arg36 is present in the prodomain and is not highly conserved. To assess structural consequences of the amino acid substitutions, both mutants were modeled within the predicted structure of the enzyme. To examine the effects of these mutations on enzyme expression and activity, we expressed the mutated enzymes in human embryonic kidney 293T cells. These analyses revealed that Asn271Ser abolished enzymatic activity, while Arg36His led to a ∼50{\%} reduction in CPA6 levels in the ECM. Pulse-chase using radio-labeled amino acids was performed to follow secretion. Newly-synthesized CPA6 appeared in the ECM with peak levels between 2-8 hours. There was no major difference in time course between wild-type and mutant forms, although the amount of radiolabeled CPA6 in the ECM was lower for the mutants. Our experiments demonstrate that these mutations in CPA6 are deleterious and provide further evidence for the involvement of CPA6 mutations in the predisposition for several types of epilepsy.",
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