103963-71-9 Purity
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The decapping exoribonuclease DXO plays a role in pre-mRNA capping quality control. In order to understand the inhibitory mechanism of DXO, the crystal structure of DXO complex with adenosine-3',5'-bisphosphate (pAp) and Mg2+ was determined at 1.8 Å resolution. The effect of pAp on DXO 5'-3' ectoribonuclease activity was also examined. Structural and biochemical studies indicate that pAp inhibits the activity of DXO by occupying the active site and acting as a competitive inhibitor.
Protein expression, purification, and crystallization
· In brief, E234A mutant protein and the wild-type enzyme were purified by Ni-NTA and gel filtration chromatography using the same protocol.
· Free enzyme crystals of DXO were obtained with the sitting-drop vapor diffusion method at 20 °C, using a reservoir solution containing 20% (w/v) PEG 3350.
· The pAp-Mg2+ complex was obtained by soaking the free enzyme crystals with 100 mM pAp and 10 mM MgCl2 for 60 min in the presence of 15% ethylene glycol.
· Crystals were flash-frozen in liquid nitrogen for diffraction analysis and data collection at 100 K.
In yeast, PAPS reductase reduces PAPS to sulfite and PAP. The crystal structure of eukaryotic PAPS reductase from yeast, whose product is bound to adenosine 3',5'-bisphosphate (PAP), is reported. The structure reveals the complete C-terminal tail bound to the active site pocket and provides additional clues to the catalytic mechanism.
Crystallization of NatiVe and SeMet PAPS Reductase
· Purified PAPS reductase was extensively dialyzed against Tris-HCl buffer and concentrated to 10 mg/mL for crystallization using Amicon spin concentrators.
· Native protein was crystallized with the presence of 5 mM TCEP and 1 mM PAPS by hanging drop vapor diffusion using 2 µL drops of protein mixed with an equal volume of reservoir buffer.
· After 3 weeks, the crystals grew to full size of about 0.25 mm × 0.2 mm × 0.15 mm. Diffraction of crystals improved significantly by soaking with DTT followed by PAP.
· Crystals were transferred and soaked in a buffer containing 10 mM DTT for 30 min and then soaked in a buffer containing 2 mM PAP for 10 min.
· The SeMetmodified protein crystals were grown by hanging drop against 30% PEG 6000 and 0.1 M HEPES, pH 7.0, and grew to about one-third the size of native crystals.