Missense variant in TPI1 (Arg189Gln) causes neurologic deficits through structural changes in the triosephosphate isomerase catalytic site and reduced enzyme levels in vivo

• Published in: Biochimica et biophysica acta. Molecular basis of disease Vol. 1865; no. 9; pp. 2257 - 2266
• Main Authors: Roland, Bartholomew P., Richards, Kristen R., Hrizo, Stacy L., Eicher, Samantha, Barile, Zackery J., Chang, Tien-Chien, Savon, Grace, Bianchi, Paola, Fermo, Elisa, Ricerca, Bianca Maria, Tortorolo, Luca, Vockley, Jerry, VanDemark, Andrew P., Palladino, Michael J.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.09.2019
• Subjects: Alleles; Amino Acid Sequence; Anemia, Hemolytic, Congenital Nonspherocytic - genetics; Anemia, Hemolytic, Congenital Nonspherocytic - pathology; Animals; Base Sequence; Carbohydrate Metabolism, Inborn Errors - genetics; Carbohydrate Metabolism, Inborn Errors - pathology; Catalytic Domain; Child, Preschool; Dimerization; Disease Models, Animal; Drosophila - metabolism; Drosophila Proteins - genetics; Drosophila Proteins - metabolism; Female; Fibroblasts - cytology; Fibroblasts - metabolism; Genomic engineering; Glycolytic enzymopathy; Humans; Mutation, Missense; Pedigree; Protein Stability; Sequence Alignment; TPI deficiency; Triose-Phosphate Isomerase - deficiency; Triose-Phosphate Isomerase - genetics; Triose-Phosphate Isomerase - metabolism; Triosephosphate isomerase; Genomic engineering; Glycolytic enzymopathy; Triosephosphate isomerase; TPI deficiency
• ISSN: 0925-4439; 1879-260X
• DOI: 10.1016/j.bbadis.2019.05.002

Mutations in the gene triosephosphate isomerase (TPI) lead to a severe multisystem condition that is characterized by hemolytic anemia, a weakened immune system, and significant neurologic symptoms such as seizures, distal neuropathy, and intellectual disability. No effective therapy is available. Here we report a compound heterozygous patient with a novel TPI pathogenic variant (NM_000365.5:c.569G>A:p.(Arg189Gln)) in combination with the common (NM_000365.5:c.315G>C:p.(Glu104Asp)) allele. We characterized the novel variant by mutating the homologous Arg in Drosophila using a genomic engineering system, demonstrating that missense mutations at this position cause a strong loss of function. Compound heterozygote animals were generated and exhibit motor behavioural deficits and markedly reduced protein levels. Furthermore, examinations of the TPIArg189Gln/TPIGlu104Asp patient fibroblasts confirmed the reduction of TPI levels, suggesting that Arg189Gln may also affect the stability of the protein. The Arg189 residue participates in two salt bridges on the backside of the TPI enzyme dimer, and we reveal that a mutation at this position alters the coordination of the substrate-binding site and important catalytic residues. Collectively, these data reveal a new human pathogenic variant associated with TPI deficiency, identify the Arg189 salt bridge as critical for organizing the catalytic site of the TPI enzyme, and demonstrates that reduced TPI levels are associated with human TPI deficiency. These findings advance our understanding of the molecular pathogenesis of the disease, and suggest new therapeutic avenues for pre-clinical trials. •We report a novel TPI pathogenic variant Arg189Gln found in a compound heterozygote patient with the “common” mutation.•Drosophila TPIR189Q is a strong loss-of-function mutation that disrupts critical TPI dimer salt bridges.•Structural studies demonstrate Arg189 is critical for the coordination of the substrate-binding site and catalytic residues.