Disease-associated mutations impacting BC-loop flexibility trigger long-range transthyretin tetramer destabilization...

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• Hereditary transthyretin amyloidosis (ATTR) is an autosomal dominant disease.
• Extracellular deposition of transthyretin (TTR) as amyloid fibrils causes ATTR.
• The molecular basis for varying clinical manifestations due to TTR mutations is not fully understood.

Purpose of the Study:

• Investigate the molecular mechanisms of ATTR caused by missense mutations at TTR residues R34 and K35.
• Determine how specific TTR variants (R34G, K35T, R34T, K35N) lead to different clinical outcomes (vitreous amyloidosis, polyneuropathy, cardiomyopathy).

Main Methods:

• Studied TTR variants R34G, K35T, R34T, and K35N.
• Assessed pH-induced dissociation and amyloid formation.
• Performed chemical denaturation experiments.
• Determined crystal structures of double mutants (R34G/T119M, K35T/T119M).
• Utilized molecular dynamics simulations.

Main Results:

• All studied TTR variants showed increased sensitivity to pH-induced dissociation and aggregation compared to wild-type (WT)-TTR.
• Variants causing vitreous amyloidosis (R34G, K35T) showed aggregation near physiological pH.
• All mutants were less stable than WT-TTR; vitreous variants were highly destabilized.
• Stabilizing the dimer-dimer interface (T119M) reduced pH-induced aggregation in R34G and K35T mutants.
• Structural and simulation data indicated that R34 and K35 mutations destabilize the TTR structure locally at the BC loop, increasing flexibility.

Conclusions:

• The study elucidates the sequence-dynamic-structural mechanisms of TTR amyloid aggregation for R34 and K35 variants.
• Mutation-induced conformational flexibility correlates with protein aggregation propensity in ATTR.
• Findings link specific TTR mutations to distinct clinical manifestations through altered protein stability and aggregation dynamics.