title: Understanding the role of argininosuccinate lyase transcript variants in the clinical and biochemical variability of the urea cycle disorder argininosuccinic aciduria.
abstract: Argininosuccinic aciduria (ASA) is an autosomal recessive urea cycle disorder caused by deficiency of argininosuccinate lyase (ASL) with a wide clinical spectrum from asymptomatic to severe hyperammonemic neonatal onset life-threatening courses. We investigated the role of ASL transcript variants in the clinical and biochemical variability of ASA. Recombinant proteins for ASL wild type, mutant p.E189G, and the frequently occurring transcript variants with exon 2 or 7 deletions were (co-)expressed in human embryonic kidney 293T cells. We found that exon 2-deleted ASL forms a stable truncated protein with no relevant activity but a dose-dependent dominant negative effect on enzymatic activity after co-expression with wild type or mutant ASL, whereas exon 7-deleted ASL is unstable but seems to have, nevertheless, a dominant negative effect on mutant ASL. These findings were supported by structural modeling predictions for ASL heterotetramer/homotetramer formation. Illustrating the physiological relevance, the predominant occurrence of exon 7-deleted ASL was found in two patients who were both heterozygous for the ASL mutant p.E189G. Our results suggest that ASL transcripts can contribute to the highly variable phenotype in ASA patients if expressed at high levels. Especially, the exon 2-deleted ASL variant may form a heterotetramer with wild type or mutant ASL, causing markedly reduced ASL activity.
authors.affiliation: From the Division of Metabolism, University Children's Hospital, 8032 Zurich, Switzerland.
authors.forename: Liyan
authors.initials: L
authors.lastname: Hu
authors.forename: Amit V
authors.initials: AV
authors.lastname: Pandey
authors.forename: Sandra
authors.initials: S
authors.lastname: Eggimann
authors.forename: Véronique
authors.initials: V
authors.lastname: Rüfenacht
authors.forename: Dorothea
authors.initials: D
authors.lastname: Möslinger
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Nuoffer
authors.forename: Johannes
authors.initials: J
authors.lastname: Häberle
mesh_terms: D000328:Adult; D001123:Argininosuccinate Lyase / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D056807:Argininosuccinic Aciduria / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D002648:Child; D005091:Exons; D005786:Gene Expression Regulation; D005838:Genotype; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D009154:Mutation; D010641:Phenotype; D020033:Protein Isoforms / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000235:genetics
chemical_list: D020033:Protein Isoforms; D011994:Recombinant Proteins; D001123:Argininosuccinate Lyase
keywords: Argininosuccinate Lyase (ASL); Argininosuccinic Aciduria (ASA); Computer Modeling; Homomeric/Heterotetrameric Protein; Metabolic Diseases; Recombinant Protein Expression; Transcript Variants; Transfection; Urea Cycle