Karl-Friedrich Bonhoeffer Award Lecture: ß-Amyloid, Microwaves and the Magic Angle

(See also the attached pdf-File for this announcement)

Nuclear magnetic resonance (NMR) is the prime tool for structure elucidation of molecules
that are difficult to study with other methods for structural biology, such as cryo-EM or X-ray
crystallography. Methodological development as well as improved instrumentation have
revolutionized what is currently possible with this method. This presentation will selectively cover
three closely related sets of experiments that have become possible because of emerging techniques:
NMR with very fast magic angle spinning (MAS), dynamic nuclear polarization (DNP) to enhance
signals by orders of magnitude, and their application to structural determination of Aß1-42, Aß1-40 and
ß2-microglobulin amyloid fibrils.
Approximately 120 years ago, Auguste Deter, the first patient diagnosed with Alzheimer’s
disease, passed away and fibrils composed of the Aß1-42 protein, the toxic species in AD, were found
postmortem in her brain. Since that time there have been numerous attempts to understand the
structure of these fibrils, but, since these species do not diffract to high resolution and are insoluble,
a true atomic resolution structure was lacking. Accordingly, we developed a suite of MAS dipolar
recoupling experiments that permit the measurement of multiple 13C-13C and 13C-15N distances and
the determination of atomic resolution structures of fibrils. We demonstrate the methodology with a
description of the high-resolution structure of fibrils of monomorphic Aß1-42, constrained by
measurement of over 500 distance restraints. We have also used these techniques to determine the
structure of Aß1-40, the second major component of Alzheimer’s disease, and ß2-microglobulin
associated with dialysis related amyloidosis
Second, to increase the signal-to-noise in MAS spectra and to better determine molecular
structures, we developed methods to perform high field dynamic nuclear polarization (DNP)
experiments. The experiments utilize sub terahertz microwaves (~150-600 GHz) generated by
gyrotron microwave sources together with paramagnetic polarizing agents to enhance the sensitivity
of MAS NMR experiments. Specifically, we irradiate electron-nuclear transitions that transfer the
large electron polarization to nuclear spins via the Overhauser, cross and solid effects. In addition,
we have recently initiated time domain DNP in order to circumvent the field dependence of CW DNP.
We show that spin locking the electrons and chirping the microwave frequency serves as an effective
approach to time domain DNP. Enhancements of 500 can be achieved, and we present applications
of DNP to Aß1-42. Future structural biology DNP experiments will likely be performed at high
spinning frequencies using MAS rotors fabricated from diamond single crystals.