Icosahedral complexes

C. C. Chancey and M. C, M. O Brien, The Jahn-Teller Effect in ttnd other Icosahedral Complexes, Princeton University Press, FYinceton, NJ, 1997. 

L. Pauling, Icosahedral quasicrystals of intermetallic compounds are icosahedral twins of cubic crystals of three kinds, consisting of large (about 5000 atoms) icosahedral complexes in either a cubic body-centered or a cubic face-centered arrangement or smaller (about 1350 atoms) icosahedral complexes in the /2-tungsten arrangement. Proc. Natl. Acad. Sci. (USA) 86, 8595-8599 (1989). 

Apart from the immune system, there is little use for the degradation products released by the proteasome, and several peptidases exist which complete their conversion into free amino acids. One of them is tricorn peptidase, originally found in Thermoplasma cells, where it exists in the form of a giant icosahedral complex of approximately 15 MDa (Tamura et al., 1996 Walz et al., 1997). It has been shown in in vitro studies that tricorn in cooperation with an array of aminopeptidases converts oligopeptides of 8-12 residues efficiently into free amino acids (Tamura et al., 1998). Tricorn peptidase has been found in a number of archaeal and bacterial species, but it is not ubiquitous functional homologs are... 

In the structure of pyruvate dehydrogenase complex, the E2 component forms the central core of the complex. PDHc from Gram-negative bacteria possesses an octahedral E2 core while the Gram-positive and eukaryotic PDHc are based on an icosahedral core [22]. The El and E3 components are attached noncovalently to the E2 core. The El component occurs in two forms depending on the symmetry of the complex. In octahedral complexes, El component is an (a,) homodimer with a subunit mass of approximately 100 kDa, while in icosahedral complexes, it exists as an (a2P2) heterotetramer with subunits of approximately 41 kDa and 36 kDa [23,24]. 

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