Sans2d data for PA28 (points) and initial simulations (lines) allowing for dimer–monomer equilibrium. D2O/H2O contrast variation with deuterated a subunits shows that the rings comprise three a and four b units.
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In biological cells, the so-called ‘20S proteasome’ is responsible for breaking down damaged or unneeded proteins so they can be recycled into new ones.
Its function is regulated by several Proteasome Activators (PAs). For example, PA28 binds to proteasomes and the resulting complex promotes the production of immune-response peptides. PA28 is known to comprise seven-membered rings containing two very similar subunits, named a and b, each of molecular weight ~28 kDa. Novel insight into the structure of PA28 has been obtained in small-angle neutron scattering (SANS) experiments carried out on the recently commissioned Second Target Station instrument Sans2d. Employing water-solvent contrast variation with deuterated a subunits was key to this study. Initial modeling efforts having as starting point the crystal structure of homologue PA28 indicate that PA28 heptamer rings are made up of three a and four b subunits in an alternating zig-zag arrangement. The SANS intensities also reveal that there is a well-defined solution equilibrium between heptamer and its double-ring dimer, making the analysis more intricate than anticipated.
M Sugiyama (Kyoto University, Japan), E Kurimoto (Meijo University, Japan), S Takata (JAEA, Japan), K Kato (Okazaki Institute for Integrative Bioscience and Institute for Molecular Science, Japan)
Research date: January 2010
Contact: Dr M Sugiyama, firstname.lastname@example.org
Further reading: M Sugiyama, in preparation
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