Microgravity crystallization of perdeuterated tryptophan synthase for neutron diffraction

Microgravity-like Crystallization of Paramagnetic Species in Strong Magnetic Fields

The crystallization of paramagnetic species in a magnetic field gradient under microgravity-like conditions is an area of interest for both fundamental and applied science. In this paper, a setup for the crystallization of paramagnetic species in the magnetic field up to 7 T generated by a superconducting magnet is described. The research includes calculations of the conditions necessary to compensate for the gravitational force for several types of paramagnetic substances using the magnetic field of superconducting magnets (4.7 T, 7 T, 9.4 T, and 16.4 T). Additionally, for the first time, the crystallization of copper sulfate and cobalt sulfate, as well as a mixture of copper sulfate and cobalt sulfate under gravitational force compensation in a superconducting magnet, was performed. This paper experimentally demonstrates the feasibility of growing paramagnetic crystals within the volume of a test tube on the example of copper and cobalt sulfate crystals. A comparison of crystals grown from the solution of a mixture of copper and cobalt sulfates under the same conditions, with and without the presence of a magnetic field, showed changes in both the number and size of crystals.

Neutron diffraction from a microgravity-grown crystal reveals the active site hydrogens of the internal aldimine form of tryptophan synthase

Pyridoxal 5'-phosphate (PLP), the biologically active form of vitamin B6, is an essential cofactor in many biosynthetic pathways. The emergence of PLP-dependent enzymes as drug targets and biocatalysts, such as tryptophan synthase (TS), has underlined the demand to understand PLP-dependent catalysis and reaction specificity. The ability of neutron diffraction to resolve the positions of hydrogen atoms makes it an ideal technique to understand how the electrostatic environment and selective protonation of PLP regulates PLP-dependent activities. Facilitated by microgravity crystallization of TS with the Toledo Crystallization Box, we report the 2.1 Å joint X-ray/neutron (XN) structure of TS with PLP in the internal aldimine form. Positions of hydrogens were directly determined in both the α- and β-active sites, including PLP cofactor. The joint XN structure thus provides insight into the selective protonation of the internal aldimine and the electrostatic environment of TS necessary to understand the overall catalytic mechanism.

Observations on Laue diffraction within synchrotron radiation and neutron macromolecular crystallography research and developments

A seminal contribution in the domain of physiologically relevant biological structure and function determination was by Keith Moffat, of Cornell and latterly of the University of Chicago proposing that synchrotrons should offer the option of a Laue method data collection mode. I enthusiastically joined in supporting this initiative. This proposal needed detailed methods development though; theoretical, experimental and software development. This work was added to the broad research and development program of synchrotron radiation at the UK's SRS. This whole program led to knowledge transfer from the UK's SRS to the ESRF as well as for neutron Laue protein crystallography to the reactor spallation sources and later to spallation neutron sources.

Public-private partnerships in fostering outer space innovations

As public and private institutions recognize the role of space exploration as a catalyst for economic growth, various areas of innovation are expected to emerge as drivers of the space economy. These include space transportation, in-space manufacturing, bioproduction, in-space agriculture, nuclear launch, and propulsion systems, as well as satellite services and their maintenance. However, the current nature of space as an open-access resource and global commons presents a systemic risk for exuberant competition for space goods and services, which may result in a "tragedy of the commons" dilemma. In the race among countries to capture the value of space exploration, NASA, American research universities, and private companies can avoid any coordination failures by collaborating in a public-private research and development partnership (PPRDP) structure. We present such a structure founded upon the principles of polycentric autonomous governance, which incorporate a decentralized autonomous organization framework and specialized research clusters. By advancing an alignment of incentives among the specified participatory members, PPRDPs can play a pivotal role in stimulating open-source research by creating positive knowledge spillover effects and agglomeration externalities as well as embracing the nonlinear decomposition paradigm that may blur the distinction between basic and applied research.

Equilibration of precipitants in a counter-diffusion apparatus for protein crystallization

A cost-effective capillary dialysis apparatus (Toledo Capillary Box, TCB) developed for biomacromolecule crystal growth in microgravity and unit gravity environments can provide slow equilibration between the precipitant reservoir and capillary solutions, nurturing growth of neutron-diffraction-quality crystals. Under microgravity conditions, mass transfer of precipitants and biomacro-mol-ecules occurs under diffusion-controlled conditions, promoting slow growth and suppressing defect formation. The equilibration of common precipitants (polyethyl-ene glycol and salts such as ammonium sulfate) between capillary and reservoir solutions was measured for capillaries oriented horizontally or vertically with respect to the gravitational field at unit gravity. Precipitants equilibrated less rapidly in the vertical orientation when capillary solution densities were lower than those of the reservoir solutions. A plug filled with agarose gel was introduced in the TCB apparatus for salt precipitants since salts often exhibit relatively high free diffusion. Equilibration of the capillaries with reservoir solutions was significantly delayed for many of the salt precipitants tested. Analytical and semi-analytical models allow the prediction of precipitant equilibration of capillary and reservoir solutions under diffusion-controlled transport and show good agreement with experimental results.