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MON-188 Characterization and Categorization Based on Genotype-Biochemical Phenotype Association in Fructose-1,6-Bisphosphatase Deficiency

Fructose-1,6-bisphosphatase (FBPase) deficiency, caused by an FBP1 mutation, is an autosomal recessive disorder characterized by hypoglycemia and metabolic acidosis. Due to the rarity of FBPase deficiency, elucidating the mechanism by which the mutations cause enzyme activity loss is challenging. We...

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Detalles Bibliográficos
Autores principales: Sakuma, Ikki, Yao, Yue, Fujimoto, Masanori, Nagano, Hidekazu, Yokote, Koutaro, Tanaka, Tomoaki
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Endocrine Society 2019
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6551122/
http://dx.doi.org/10.1210/js.2019-MON-188
Descripción
Sumario:Fructose-1,6-bisphosphatase (FBPase) deficiency, caused by an FBP1 mutation, is an autosomal recessive disorder characterized by hypoglycemia and metabolic acidosis. Due to the rarity of FBPase deficiency, elucidating the mechanism by which the mutations cause enzyme activity loss is challenging. We performed whole-exome sequencing in an adult patient with severe hypoglycemic lactic acidosis and identified that the patient carried compound heterozygous missense mutations of FBP1 (NM_000507.3) with c.491G>A (p.G164D) and c.581T>C (p.F194S). Biochemical analysis using FBP1-KO HepG2 cells generated by CRISPR/Cas9 system revealed that FBP1 mutant (G164D or F194S) overexpression decreased protein expression and enzyme activity loss. The interactome analysis based on Liquid chromatography-tandem MS data for binding partners demonstrated that FBP1, particularly its mutant, interacts with the proteins involved in the molecular chaperone related to unfolded protein response including heat shock protein (HSP). Indeed, G164D and F194S mutants exhibited increased HSPs interaction and aggregated in the endoplasmic reticulum, suggesting involvement of protein misfolding in its pathogenesis. The biochemical phenotypes of all FBP1 missense mutations previously reported were examined and categorized into three functional phenotypes: Type 1 mutations, located at pivotal residues in enzyme activity motifs with no effects on protein expression and intracellular localization; Type 2 mutations, which mediate changes in amino acid hydrophobicity and structurally cluster around the substrate binding pocket, are associated with high HSP-binding, aggregation in the endoplasmic reticulum, and decreased protein expression; and Type 3 mutations, which are likely non-pathogenic mutations without biochemical phenotype. Thus, our findings demonstrate that protein misfolding contributes to FBPase deficiency pathogenesis, particularly in Type 2 mutations; therefore, its missense mutations can be classified into three categories based on genotype functional phenotype association.