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Structural insight into pH-induced conformational changes within the native human transthyretin tetramer
Satheesh K Palaninathan1, Nilofar N Mohamedmohaideen, William C Snee
1Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843, USA.
Acidification of transthyretin (TTR) causes structural changes, particularly in the EF helix-loop region, leading to tetramer destabilization and amyloid fiber formation. These findings reveal key early steps in TTR amyloidogenesis.
Area of Science:
- Biochemistry
- Structural Biology
- Protein Folding
Background:
- Transthyretin (TTR) amyloidosis is linked to protein misfolding and aggregation.
- Acidification is known to promote TTR tetramer dissociation and amyloid formation.
- Understanding structural changes at the molecular level is crucial for TTR amyloidogenesis research.
Purpose of the Study:
- To investigate the impact of acidic pH on the quaternary and tertiary structures of wild-type human TTR.
- To elucidate the initial conformational changes in TTR that precede amyloid fiber formation.
Main Methods:
- Determination of crystal structures of wild-type human TTR at pH 4.0 and pH 3.5 to 1.7 A resolution.
- Comparison of acidic pH structures with the previously determined wild-type TTR pH 7.4 structure.
Main Results:
- At pH 4.0, TTR subunit B shows significant conformational changes in the EF-helix and EF-loop region compared to native TTR.
- Acidic residues (Glu72, Asp74, Glu89, Glu92) undergo conformational shifts, influencing nearby residues and hydrophobic pockets.
- At pH 3.5, the EF helix-loop region of TTR subunit B is completely disordered, indicating significant destabilization.
Conclusions:
- Acidic conditions destabilize the TTR tetramer by inducing conformational changes in the EF helix-loop region.
- These changes increase the susceptibility of TTR monomers to unfold, initiating the pathway towards amyloidogenic aggregation.
- The study identifies critical early structural events in TTR amyloidogenesis.
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