Unusual duplication mutation in a surface loop of human transthyretin leads to an aggressive drug-resistant amyloid disease.

Abstract

Transthyretin (TTR) is a globular tetrameric transport protein in plasma. Nearly 140 single amino acid substitutions in TTR cause life-threatening amyloid disease. We report a one-of-a-kind pathological variant featuring a Glu51, Ser52 duplication mutation (Glu51_Ser52dup). The proband, heterozygous for the mutation, exhibited an unusually aggressive amyloidosis that was refractory to treatment with the small-molecule drug diflunisal. To understand the poor treatment response and expand therapeutic options, we explored the structure and stability of recombinant Glu51_Ser52dup. The duplication did not alter the protein secondary or tertiary structure but decreased the stability of the TTR monomer and tetramer. Diflunisal, which bound with near-micromolar affinity, partially restored tetramer stability. The duplication had no significant effect on the free energy and enthalpy of diflunisal binding, and hence on the drug-protein interactions. However, the duplication induced tryptic digestion of TTR at near-physiological conditions, releasing a C-terminal fragment 49-129 that formed amyloid fibrils under conditions in which the full-length protein did not. Such C-terminal fragments, along with the full-length TTR, comprise amyloid deposits in vivo. Bioinformatics and structural analyses suggested that increased disorder in the surface loop, which contains the Glu51_Ser52dup duplication, not only helped generate amyloid-forming fragments but also decreased structural protection in the amyloidogenic residue segment 25-34, promoting misfolding of the full-length protein. Our studies of a unique duplication mutation explain its diflunisal-resistant nature, identify misfolding pathways for amyloidogenic TTR variants, and provide therapeutic targets to inhibit amyloid fibril formation by variant TTR.

• Authors: Elena S Klimtchuk, Tatiana Prokaeva, Nicholas M Frame, Hassan A Abdullahi, Brian Spencer, Surendra Dasari, Haili Cui, John L Berk, Paul J Kurtin, Lawreen H Connors, Olga Gursky
• Journal: Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 115 Issue 28 Pg. E6428-E6436 (07 10 2018) ISSN: 1091-6490 [Electronic] United States
• PMID: 29941560 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Amyloid
• Prealbumin
• Diflunisal

Topics

• Amyloid (chemistry, genetics, metabolism)
• Amyloid Neuropathies, Familial (drug therapy, genetics, metabolism)
• Diflunisal (therapeutic use)
• Drug Resistance
• Female
• Humans
• Male
• Models, Molecular
• Mutation
• Prealbumin (chemistry, genetics, metabolism)
• Protein Structure, Secondary