title: S81L and G170R mutations causing Primary Hyperoxaluria type I in homozygosis and heterozygosis: an example of positive interallelic complementation.
abstract: Primary Hyperoxaluria type I (PH1) is a rare disease due to the deficit of peroxisomal alanine:glyoxylate aminotransferase (AGT), a homodimeric pyridoxal-5'-phosphate (PLP) enzyme present in humans as major (Ma) and minor (Mi) allele. PH1-causing mutations are mostly missense identified in both homozygous and compound heterozygous patients. Until now, the pathogenesis of PH1 has been only studied by approaches mimicking homozygous patients, whereas the molecular aspects of the genotype-enzymatic-clinical phenotype relationship in compound heterozygous patients are completely unknown. Here, for the first time, we elucidate the enzymatic phenotype linked to the S81L mutation on AGT-Ma, relative to a PLP-binding residue, and how it changes when the most common mutation G170R on AGT-Mi, known to cause AGT mistargeting without affecting the enzyme functionality, is present in the second allele. By using a bicistronic eukaryotic expression vector, we demonstrate that (i) S81L-Ma is mainly in its apo-form and has a significant peroxisomal localization and (ii) S81L and G170R monomers interact giving rise to the G170R-Mi/S81L-Ma holo-form, which is imported into peroxisomes and exhibits an enhanced functionality with respect to the parental enzymes. These data, integrated with the biochemical features of the heterodimer and the homodimeric counterparts in their purified recombinant form, (i) highlight the molecular basis of the pathogenicity of S81L-Ma and (ii) provide evidence for a positive interallelic complementation between the S81L and G170R monomers. Our study represents a valid approach to investigate the molecular pathogenesis of PH1 in compound heterozygous patients.
authors.affiliation: Department of Life Sciences and Reproduction, University of Verona, Verona, Italy and.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Montioli
authors.affiliation: Department of Life Sciences and Reproduction, University of Verona, Verona, Italy and.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Roncador
authors.affiliation: Department of Life Sciences and Reproduction, University of Verona, Verona, Italy and.
authors.forename: Elisa
authors.initials: E
authors.lastname: Oppici
authors.affiliation: Department of Clinical and Biological Sciences, University of Torino, Torino, Italy.
authors.forename: Giorgia
authors.initials: G
authors.lastname: Mandrile
authors.affiliation: Department of Clinical and Biological Sciences, University of Torino, Torino, Italy.
authors.forename: Daniela Francesca
authors.initials: DF
authors.lastname: Giachino
authors.affiliation: Department of Life Sciences and Reproduction, University of Verona, Verona, Italy and barbara.cellini@univr.it.
authors.forename: Barbara
authors.initials: B
authors.lastname: Cellini
authors.affiliation: Department of Life Sciences and Reproduction, University of Verona, Verona, Italy and.
authors.forename: Carla
authors.initials: C
authors.lastname: Borri Voltattorni
mesh_terms: D000293:Adolescent; D000328:Adult; D000483:Alleles; D019943:Amino Acid Substitution; D005260:Female; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D006960:Hyperoxaluria, Primary / Q000201:enzymology* / Q000235:genetics*; D008297:Male; D020125:Mutation, Missense; D021381:Protein Transport; D000637:Transaminases / Q000235:genetics* / Q000378:metabolism
chemical_list: D000637:Transaminases; C023067:glyoxylate aminotransferase