Crystallization and preliminary structural study of the Thermobaculum terrenum Csh2 in the type IB CRISPR system

CRISPR/Cas system is an RNA-mediated prokaryotic adaptive immune system against mobile genetic elements. Among three CRISPR/Cas systems, type I system has two functional units in removing nucleic acids, Cascade and Cas3. Type IB Cascade has been analyzed to have components of Csh1, Csh2, Cas4, and Cas5, whose structural and functional information is not available. To provide a structural background for the type IB Cascade, the preliminary structural study of the Csh2 from Thermobaculum terrenum is reported here. The purified recombinant protein was successfully crystallized using the precipitant solution composed of 10% (w/v) Polyethylene Glycol 3350, 2% (v/v) Tacsimate at pH 5.0, and 100 mM Sodium Citrate tribasic dihydrate at pH 5.6. Diffraction data were collected to a resolution of 1.93 Å using synchrotron radiation. The crystal belongs to the primitive triclinic P1 space group, with unit cell dimensions a = 31.04 Å, b = 54.65 Å, c = 96.46 Å, α = 73.6 º, β = 88.4 º and γ = 89.8 º. With two molecules in the asymmetric unit, the crystal volume per unit protein weight corresponds with 2.29 Å 3 ·Da -1 , resulting in 46% solvent.