Figure 5.

Pseudorotation cycle of the pentofuranose ring in nucleosides. Sectors are named as ⁱT_j and _iT^j for unsymmetrical twist conformations (the character of atomic displacements from the mean plane of the ring is preserved in each sector). Pseudorotation angles of purine nucleosides and their analogs in the active sites of hexameric PNPs in the presence of sulfate (phosphate) ions are shown in red, while when sulfate (phosphate) ions are absent they are shown in green. Pseudorotation angles of purine nucleosides and their analogs in the active sites of trimeric PNPs in the presence of sulfate (phosphate) ions are shown in violet, while when sulfate (phosphate) ions are absent they are shown in blue. Pseudoratation angles of uridine or thymidine in the active sites of UP in the presence of sulfate ions are shown as yellow, while when sulfate ions are absent they are shown as light pink.