TOPICAL subunit structure

Despite the unity in secondary structural patterns, little is known about the three-dimensional, or tertiary, structure of rRNAs. Even less is known about the quaternary interactions that occur when ribosomal proteins combine with rRNAs and when the ensuing ribonucleoprotein complexes, the small and large subunits, come together to form the complete ribosome. Furthermore, assignments of functional roles to rRNA molecules are still tentative and approximate. (We return to these topics in Chapter 33.)... 

Proteins containing more than one polypeptide chain, such as hemoglobin (see Topic B4), exhibit a fourth level of protein structure called quaternary structure (Fig. 8). This level of structure refers to the spatial arrangement of the polypeptide subunits and the nature of the interactions between them. These interactions may be covalent links (e.g. disulfide bonds) or noncovalent interactions (electrostatic forces, hydrogen bonding, hydrophobic interactions). 

Additionally, supramolecular carbon nanostructures have been made from nanoballs, -rods, and -tubes. New materials can be formed with the different nanosized structures but preparation of their materials and properties is somewhat different than for traditional materials. For example, nanocrystalline metals are much harder. These materials and unusual properties combine to create composites, for example, from the co-deposition of particles with metals in a plating process or in compositionally modulated multi-layers. Also of interest are core-shell particles, which consist of an inorganic core and a conducting polymer shell, and the traditional composites with larger subunits. Ways leading to the preparation of such nanocomposites is an interesting topic and will be discussed in this chapter. 

Self-Association of Proteins The idea that many proteins are non-covalent complexes of two or more identical subunits can be traced back to the early work of Svedberg with the analytical ultracentrifuge (ref. 4). Such protein assembly is referred to as quaternary structure, a topic reviewed by Klotz et al. in 1970 (ref. 5). 

Sebald W, Hoppe J (1982) On the structure and genetics of the proteolipid subunit of the ATPsynthase complex. In Current topics in bioenergetics, Sanadi DR,ed., vol. 12, p. 1-64, Academic Press, New York... 

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