Fig. 2: Spore proteasome active sites are blocked by PI31-like peptides.
From: Structure of the reduced microsporidian proteasome bound by PI31-like peptides in dormant spores
a Overview of PI31L (red solid and orange transparent cryo-EM densities) in the context of the full proteasome (left) and views of the two β-rings, next to selected PI31L-bound β-subunits. The selected proteasome subunits are shown with surface representations, colored in shades of blue and superimposed with the cryo-EM densities of PI31L (red, orange). Subunits marked by a black dot highlight those responsible for proteolysis. b Cryo-EM density and model fit of one PI31L peptide, with selected residues labeled. c Domain architectures of the two PI31L peptides are shown above a sequence alignment of the C-terminal domain of the identified microsporidian PI31L peptides with a selection of eukaryotic PI31. Modeled sections are indicated with colored bars or red squared sequence stretches, while disordered loops are depicted with dotted lines. (a, b, c) The location where PI31L traverses into the opposite ring is indicated with dotted lines and an orange/red circle. d Zoom-in sections of active sites of the proteolytically active β-subunits. The β-subunits are shown as surfaces colored as in (a), with the active-site threonine highlighted in yellow and PI31L as red cartoon with selected residues as sticks. The yeast PI31 structure (PDB-7TEO10 [https://www.rcsb.org/structure/7TEO]) is superimposed and shown in shades of green. e A schematic representation of proteolytic active sites and specificity sites, with active site threonines shown in yellow and PI31 orientations shown in red (V. necatrix) or green (S. cerevisiae). Residues conserved in yeast and V. necatrix are circled in black.
