Heptameric rings

A further striking example is given by the Pyrococcus abyssi Sm core (PA Sm). In the free state and in complex with RNA, the PA Sm has point symmetry 72 and consists of a sandwich of two heptameric rings in the same orientation and dyadically related [20]. In the two states, the folding of the monomers differs only slightly, so that the corresponding molecular forms of PA Sm heptamer (central hole and envelope) are the same. 

Figure 11-5. The form lattice of the double heptameric ring of the pyrococcus abyssi Sm core in the free state conformation is isometric heptagonal. The lattice parameter is given by the distance u of each heptamer from a twofold axis (from [16], courtesy lUCr)...

Figure 11-6. The double heptameric ring of pyrococcus abyssi Sm core in complex with RNA (not shown) has the same form lattice as in the free state. Only the distance d between the heptamers is doubled d = Au instead of 2u (from [19], courtesy lUCr)...

The 14 subunits arrange as two heptameric rings, that is, with 7 units having a C7 symmetry axis, related to the second 7 units by a twofold dyad axis. This results in two water-filled cavities of 85,000 each. Each of the 14 subunits consists of three domains—an equatorial domain, an intermediate domain, and an apical domain. Seven ATP molecules bind to the 7 equatorial domains at a position near the intermediate domain and, in our view by means of AG,p, propagate dissociations of hydrophobic domains (including their intrinsic ion pairs) and domain rotations in the intermediate and apical domains due to apolar-polar repulsions. The result is a water-filled cavity with its size doubled to 175,000 A . ... 

Figure 3.3 The proteasome. The proteasome is composed of two primary components the 20S catalytic particle and the 19S regulatory particle. The 20S catalytic particle is made up of two pair of heptameric rings, a (outer) and P (inner), and contains the catalytic sites for protein degradation. The 19S regulatory particle is coupled to the 20S catalytic particle at either end, to make up the 26S proteasome. The 19S regulatory particle is responsible for substrate recognition, and the ATP-dependent unfolding of proteins necessary for entrance into the catalytic core.

The complementary nature of ESI-MS and ESI-IMS is illustrated in Figure 18.11. The proteasome is an intracellular protease complex that is responsible for degradation of most imfolded proteins in the cytosol and in the nucleus. The 20S proteasome is composed of four heptameric rings stacked in a barrel fashion, forming an internal cavity where... 

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