Microgravity crystallization of perdeuterated tryptophan synthase for neutron diffraction

摘要: Biologically active vitamin B6-derivative pyridoxal 5′-phosphate (PLP) is an essential cofactor in amino acid metabolic pathways. PLP-dependent enzymes catalyze a multitude of chemical reactions but, how reaction diversity of PLP-dependent enzymes is achieved is still not well understood. Such comprehension requires atomic-level structural studies of PLP-dependent enzymes. Neutron diffraction affords the ability to directly observe hydrogen positions and therefore assign protonation states to the PLP cofactor and key active site residues. The low fluxes of neutron beamlines require large crystals (≥0.5 mm3). Tryptophan synthase (TS), a Fold Type II PLP-dependent enzyme, crystallizes in unit gravity with inclusions and high mosaicity, resulting in poor diffraction. Microgravity offers the opportunity to grow large, well-ordered crystals by reducing gravity-driven convection currents that impede crystal growth …