Simultaneously Measured Kinetics of Two Amyloid Polymorphs Using Cross Peak Specific 2D IR Spectroscopy

Area of Science:

• Biophysics
• Biochemistry
• Materials Science

Background:

• Amyloid fibril polymorphism is poorly understood due to limitations in monitoring multiple polymorph formation kinetics simultaneously.
• Human islet amyloid polypeptide (hIAPP) is a key protein implicated in type 2 diabetes, forming amyloid fibrils.

Purpose of the Study:

• To investigate the origin and kinetics of amyloid fibril polymorphs using advanced spectroscopic techniques.
• To differentiate polymorphic structures formed through different nucleation pathways.

Main Methods:

• Utilized a novel cross-peak specific polarization scheme (⟨0°,0°,60°,-60°⟩) with 2D Infrared (2D IR) spectroscopy.
• Analyzed 2D IR spectra of hIAPP amyloid fibrils to resolve previously unseen cross peaks.
• Simulated fibril formation kinetics using three distinct models, including secondary nucleation.

Main Results:

• Resolved 22 new cross peaks in the 2D IR spectra of hIAPP fibrils.
• Identified a subset of cross peaks corresponding to a second fibril polymorph forming on a slower timescale.
• Found that only a secondary nucleation model accurately reproduced the observed cross-peak kinetics.

Conclusions:

• Secondary nucleation generates amyloid fibrils with a distinct polymorphic structure compared to parent fibrils.
• The developed cross-peak specific polarization scheme offers enhanced structural resolution for studying amyloid polymorphism.
• This work provides critical insights into the mechanisms driving amyloid fibril heterogeneity.