Hydrogen-bond network and pH sensitivity in human transthyretin

Area of Science:

• Structural biology
• Biophysics
• Biochemistry

Background:

• Transthyretin (TTR) tetramer dissociation is key to amyloid disease formation.
• Low pH conditions are known to trigger TTR dissociation and amyloid fibril aggregation.

Purpose of the Study:

• To elucidate the molecular mechanisms of pH sensitivity in TTR.
• To understand the structural basis for TTR stability and its relation to amyloidosis.

Main Methods:

• Neutron diffraction studies using the IBARAKI Biological Crystal Diffractometer.
• Time-of-flight method for neutron data collection.
• Crystal growth up to 2.5 mm³ over four months.

Main Results:

• The 2.0 Å neutron crystal structure revealed specific protonation states of His88.
• A detailed hydrogen-bond network dependent on His88 protonation was identified.
• Acidification-induced His88 double protonation breaks this network, destabilizing the TTR tetramer.
• Comparison with X-ray structures identified three residues responsible for TTR's pH sensitivity.

Conclusions:

• The identified hydrogen-bond network and His88 protonation are critical for TTR tetramer stability.
• Neutron diffraction provides crucial insights into TTR's pH-dependent structural dynamics.
• Understanding these mechanisms can inform strategies against TTR amyloidosis.