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![[Figure 7]](rr5133fig7mag.jpg)
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Figure 7
Comparison of the binding sites for the PI-PLCs. Stereo diagrams show superposition of the binding site of the complex of PsPI-PLC with myo-inositol (gold) on the corresponding regions of (a) SanPI-PLC (PDB entry 3h4x, green), (b) the complex of BcPI-PLC with myo-inositol (PDB entry 1ptg, purple) and the BtPI-PLC R69D mutant (PDB entry 1t6m, ice blue) and (c) the complex of rat PI-PLC with D-myo-inositol-1,4,5-trisphosphate (PDB entry 1djx, pink). Protein residues are shown as cylinders, ligands in ball-and-stick representation and calcium ions as spheres. Residues used in the superpositions belong to the X-box domains (Table 2 ![[link]](../../../../../../logos/arrows/d_arr.gif) ). In all panels the catalytic His26 and His70 of PsPI-PLC are in similar locations to their counterparts in the matched structures. The best alignment for His70 (the general acid) is achieved in (c) in the superposition with rat PI-PLC. The planes of His26 (possible general base) in the PsPI-PLC structure and its counterpart (His311) in rat PI-PLC have different orientations, possibly because inositol is not phosphorylated in the former structure, while the 1-phosphate is present and makes a hydrogen bond to His311 in the latter. In (c) Glu48 in PsPI-PLC is seen to align perfectly with Glu341 in rat PI-PLC (a candidate for the general base in the mammalian enzymes; Essen et al., 1997), but has no clear counterpart in the wild-type bacterial enzymes (a, b). The difference in the position of the inositol O2 between PsPI-PLC and rat PI-PLC can be attributed to the lack of a 1-phosphate in the former. Ca2+ is present only in PsPI-PLC, rat PI-PLC and the BtPI-PLC R69D mutant and superposes most closely in the first two. Overall, the PsPI-PLC active site has more similarity to the active site of the rat enzyme (c) than the bacterial enzymes (a, b), suggesting a mammalian-like catalytic mechanism for PsPI-PLC. |
![[Figure 7]](rr5133fig7.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
