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Oligomeric symmetry of purine nucleoside phosphorylases

Many enzymes are composed of several identical subunits which are arranged in some regular fashion and usually comply with some definite symmetry. [1] This symmetry may be approximate or exact and may or may not coincide with the symmetry of crystallographic packing. Purine nucleoside phosphorylases (PNP) are one class of oligomeric enzymes that show interesting properties connected with the interplay of symmetry. [2] There are two main classes of this enzyme: trimeric PNP or “low molecular mass” protein which can be found mostly in eukaryotic organisms, and hexameric PNP or “high molecular mass” protein which can mostly be found in prokaryotic organisms (Figure 1). [3] Interestingly, these two enzyme classes share only 20-30% sequence identity, but the overall fold of the single monomer is similar, and yet this similar monomeric building block makes a different quaternary structure. As part of the ALOKOMP project (alokomp.irb.hr) which tries to understand the allosteric communication between these monomeric subunits, the relational database of PNPs is constructed. As a special subset of this database, an all-to- all overlap of these structures is also made, which makes possible the assessment of symmetry relations in these enzymes using programmatic methods.

Oligomeric proteins ; purine nucleoside phosphorylases ; Symmetry

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