Fig. 4: The putative catalytic active site of BPSL1038 dimer.
a The D11(X20) SST motif forming a negatively charged cage coordinating a well-ordered water residue (w1). The distance between the D11 and w1 for subunit A and B are 3.2 Å and 3.6 Å, respectively. The typical ST-turn motif of BPSL1038 involved S32, S33 and T34 was boxed. b The SSM superposition of BPSL1038 with Enterococcus faecalis TX0027 Cas1-Cas2-prespacer DNA complex (PDB ID: 5XVN) (light blue) shows that the putative active site region of BPSL1038 shares high similarity to the D13 and S43 residues of Efa_Cas2 that coordinate with two Mg2+ ions (magenta) for prespacer DNA backbone contact20. The overall homodimeric structure of BPSL1038 is similar to the Efa_Cas2 with a r.m.s.d of 3.3 Å over 140 aligned Cα atoms.
