Engineering Papers⌕ Search

Engineering topics

Myles, Dean A. A.

Publications and source records attributed to Myles, Dean A. A..

5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Revealing the atomic and electronic mechanism of human manganese superoxide dismutase product inhibition

Human manganese superoxide dismutase (MnSOD) is a crucial oxidoreductase that maintains the vitality of mitochondria by converting superoxide (O 2 •– ) to molecular oxygen (O 2 ) and hydrogen peroxide (H 2 O 2 ) with proton-coupled electron transfers (PCETs). Human MnSOD has evolved to be highly product inhibited to limit the formation of H 2 O 2 , a freely diffusible oxidant and signaling molecule. The product-inhibited complex is thought to be composed of a peroxide (O 2 2– ) or hydroperoxide (HO 2 – ) species bound to Mn ion and formed from an unknown PCET mechanism. PCET mechanisms of proteins are typically not known due to difficulties in detecting the protonation states of specific residues that coincide with the electronic state of the redox center. To shed light on the mechanism, we combine neutron diffraction and X-ray absorption spectroscopy of the product-bound, trivalent, and divalent states of the enzyme to reveal the positions of all the atoms, including hydrogen, and the electronic configuration of the metal ion. The data identifies the product-inhibited complex, and a PCET mechanism of inhibition is constructed.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

EWALD: A macromolecular diffractometer for the second target station

Revealing the positions of all the atoms in large macromolecules is powerful but only possible with neutron macromolecular crystallography (NMC). Neutrons provide a sensitive and gentle probe for the direct detection of protonation states at near-physiological temperatures and clean of artifacts caused by x rays or electrons. Currently, NMC use is restricted by the requirement for large crystal volumes even at state-of-the-art instruments such as the macromolecular neutron diffractometer at the Spallation Neutron Source. EWALD’s design will break the crystal volume barrier and, thus, open the door for new types of experiments, the study of grand challenge systems, and the more routine use of NMC in biology. EWALD is a single crystal diffractometer capable of collecting data from macromolecular crystals on orders of magnitude smaller than what is currently feasible. The construction of EWALD at the Second Target Station will cause a revolution in NMC by enabling key discoveries in the biological, biomedical, and bioenergy sciences.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

High-intensity X-ray beams can influence the kinetics in a time-resolved experiment

X-ray induced structural damage is well known, but the potential for changes in the kinetics of physical and chemical processes is rarely recognized or considered. These can happen over a wide intensity range, are difficult to predict and often escape detection. Subsequently, the problem deserves more attention from experimentalists.

47 OTHER INSTRUMENTATION↗
NASA NTRS2006

A Quasi-Laue Neutron Crystallographic Study of D-Xylose Isomerase

Hydrogen atom location and hydrogen bonding interaction determination are often critical to explain enzymatic mechanism. Whilst it is difficult to determine the position of hydrogen atoms using X-ray crystallography even with subatomic (less than 1.0 Angstrom) resolution data available, neutron crystallography provides an experimental tool to directly localise hydrogeddeuteriwn atoms in biological macromolecules at resolution of 1.5-2.0 Angstroms. Linearisation and isomerisation of xylose at the active site of D-xylose isomerase rely upon a complex hydrogen transfer. Neutron quasi-Laue data were collected on Streptomyces rubiginosus D-xylose isomerase crystal using the LADI instrument at ILL with the objective to provide insight into the enzymatic mechanism (Myles et al. 1998). The neutron structure unambiguously reveals the protonation state of His 53 in the active site, identifying the model for the enzymatic pathway.

Meilleur, Flora↗