title: Naturally occurring carboxypeptidase A6 mutations: effect on enzyme function and association with epilepsy.
abstract: Carboxypeptidase A6 (CPA6) is a member of the A/B subfamily of M14 metallocarboxypeptidases that is expressed in brain and many other tissues during development. Recently, two mutations in human CPA6 were associated with febrile seizures and/or temporal lobe epilepsy. In this study we screened for additional CPA6 mutations in patients with febrile seizures and focal epilepsy, which encompasses the temporal lobe epilepsy subtype. Mutations found from this analysis as well as CPA6 mutations reported in databases of single nucleotide polymorphisms were further screened by analysis of the modeled proCPA6 protein structure and the functional role of the mutated amino acid. The point mutations predicted to affect activity and/or protein folding were tested by expression of the mutant in HEK293 cells and analysis of the resulting CPA6 protein. Common polymorphisms in CPA6 were also included in this analysis. Several mutations resulted in reduced enzyme activity or CPA6 protein levels in the extracellular matrix. The mutants with reduced extracellular CPA6 protein levels showed normal levels of 50-kDa proCPA6 in the cell, and this could be converted into 37-kDa CPA6 by trypsin, suggesting that protein folding was not greatly affected by the mutations. Interestingly, three of the mutations that reduced extracellular CPA6 protein levels were found in patients with epilepsy. Taken together, these results provide further evidence for the involvement of CPA6 mutations in human epilepsy and reveal additional rare mutations that inactivate CPA6 and could, therefore, also be associated with epileptic phenotypes.
authors.affiliation: Department of Neuroscience, Albert Einstein College of Medicine,Bronx, New York 10461,USA.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Sapio
authors.forename: Annick
authors.initials: A
authors.lastname: Salzmann
authors.forename: Monique
authors.initials: M
authors.lastname: Vessaz
authors.forename: Arielle
authors.initials: A
authors.lastname: Crespel
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Lyons
authors.forename: Alain
authors.initials: A
authors.lastname: Malafosse
authors.forename: Lloyd D
authors.initials: LD
authors.lastname: Fricker
mesh_terms: D000293:Adolescent; D000328:Adult; D000483:Alleles; D043422:Carboxypeptidases A / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D016022:Case-Control Studies; D002648:Child; D003710:Demography; D004792:Enzyme Precursors / Q000378:metabolism; D004795:Enzyme Stability / Q000187:drug effects; D004827:Epilepsy / Q000201:enzymology* / Q000235:genetics*; D005190:Family; D005260:Female; D020022:Genetic Predisposition to Disease; D005820:Genetic Testing; D057809:HEK293 Cells; D006358:Hot Temperature; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008297:Male; D008958:Models, Molecular; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D014357:Trypsin / Q000378:metabolism
chemical_list: D004792:Enzyme Precursors; D050505:Mutant Proteins; D006861:Hydrogen Peroxide; C578288:CPA6 protein, human; D043422:Carboxypeptidases A; D014357:Trypsin