IMAGINE: neutrons reveal enzyme chemistry

Abstract

Neutron diffraction is exquisitely sensitive to the positions of H atoms in protein crystal structures. IMAGINE is a high-intensity, quasi-Laue neutron crystallography beamline developed at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. This state-of-the-art facility for neutron diffraction has enabled detailed structural analysis of macromolecules. IMAGINE is especially suited to resolve individual H atoms in protein structures, enabling neutron protein structures to be determined at or near atomic resolutions from crystals with volumes of less than 1 mm and unit-cell edges of less than 150 Å. Beamline features include elliptical focusing mirrors that deliver neutrons into a 2.0 × 3.2 mm focal spot at the sample position, and variable short- and long-wavelength cutoff optics that provide automated exchange between multiple wavelength configurations. This review gives an overview of the IMAGINE beamline at the HFIR, presents examples of the scientific questions being addressed at this beamline, and highlights important findings in enzyme chemistry that have been made using the neutron diffraction capabilities offered by IMAGINE.

Titration of ionizable groups in proteins using multiple neutron data sets from a single crystal: application to the small GTPase Ras

“…Using one crystal, three quasi-Laue neutron data sets were collected on the IMAGINE beamline at the High Flux Isotope Reactor, Oak Ridge National Laboratory using a narrowbandpass 3.3-4.5 Å optical configuration ( peak ' 3.9 Å , d/ ' 30%; Meilleur et al, 2013;Schrö der et al, 2018). Longer wavelengths than typically used on this instrument were selected to reduce the number of spatial overlaps.…”

Hydrogen/deuterium exchange behavior in tetragonal hen egg-white lysozyme crystals affected by solution state

“…The neutron data were collected at room temperature with a Laue diffractometer (CG-4D's IMAGINE) installed at the High Flux Isotope Reactor at Oak Ridge National Laboratory (Meilleur et al, 2013;Schrö der et al, 2018). The data were processed using LAUEGEN and normalized and merged with the LSCALE and SCALA programs (Helliwell et al, 1989;Campbell, 1995;Campbell et al, 1998;Arzt et al, 1999;Weiss, 2001).…”

The Neutron Macromolecular Crystallography Instruments at Oak Ridge National Laboratory: Advances, Challenges, and Opportunities

“…The neutron wavelength and bandpass delivered to the sample can be varied remotely by motorized translation of three neutron flat mirrors and three pairs of neutron filters that provide short wavelength (λ min = 2.0, 2.8, and 3.3 Å) and long wavelength (λ max = 3.0, 4.0, and 4.5 Å) cut-offs, respectively. A pair of elliptically-shaped mirrors then collects and focuses the resulting beam vertically and horizontally down to 2 × 3.2 mm 2 at the sample position, with full width vertical and horizontal divergence of 0.5 • and 0.6 • , respectively, and delivery of 3 × 10 7 n/s/cm 2 in standard 2.8-4.0 Å quasi-Laue configuration [2,3]. Complete specifications of the IMAGINE instrument are listed in Table 2.…”

“…At the atomic level, neutron diffraction is uniquely able to determine the location of individual hydrogen atoms in biological materials. This provides fundamental insight and mechanistic understanding of, for example, catalytic processes in enzymes, or of the proton shuttling/relay pathways involved in biological processes [2]. A major limitation, however, is that the inherent flux of neutron beams (10 6 -10 8 neutrons cm −2 s −1 ) is orders of magnitude less than conventional X-ray beams, requiring larger crystals (>0.1 mm 3 ) and extended data collection times (days or weeks) compared to those typical for X-ray analysis.…”