Proteasome

Four stacked rings of seven subunits each, capped at both ends, carrying three different cutting specificities in one machine.

Size and composition

a 2.5 megadalton complex: one catalytic core particle with two terminal regulatory particles, which associate with the core's two ends in opposite orientations

mammalian, general · review of structural work · Tanaka K 2013, Keio J Med · source

Core particle architecture

four axially stacked heptameric rings, two outer alpha and two inner beta, each of seven structurally related but not identical subunits

mammalian, general · review of structural work · Tanaka K 2013, Keio J Med · source

Three specificities in one chamber

catalytic threonines sit on beta1, beta2 and beta5, giving caspase-like, trypsin-like and chymotrypsin-like activity respectively, on the surface of the chamber formed by the two abutting beta rings

mammalian, general · review of structural work · Tanaka K 2013, Keio J Med · source

The 20S core is not one thing

the three active-site beta subunits can be replaced wholly or partly by immuno-subunits, giving standard, immuno and intermediate proteasomes, and post-translational modification and genetic variation multiply each of those into subtypes

mammalian cells and tissues · review · Dahlmann B 2016, Arch Biochem Biophys · source

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Number per cell

no abstract read for this page states a count per human cell with its method.

Dimensions in nanometres

the copy is drawn at about 15 nm across, which is the conventional figure and is not yet tied to a measurement read in an abstract on this page.

Behind the copy

The 26S proteasome is a 2.5 megadalton complex that degrades most intracellular protein. Its catalytic core particle is built from four axially stacked heptameric rings, two outer alpha rings and two inner beta rings, each made of seven structurally related but not identical subunits. A regulatory particle caps each end of the core, associating with the two termini in opposite orientations. The catalytic threonines sit on three of the beta subunits inside the chamber: beta1 is caspase-like, beta2 trypsin-like, and beta5 chymotrypsin-like, so one machine carries three different cutting specificities.

source 1

Other organelles

All · Autophagosome · Centrosome · Cilia and flagella · Cytoskeleton · Endosomes and vesicles · Golgi · Lipid droplet · Lysosome · Mitochondrion · Nuclear envelope · Nucleolus · Nucleus · Peroxisome · Plasma membrane · Ribosome · Rough ER · Smooth endoplasmic reticulum

Building the copy.