Oligomeric structures, formation

Before eomparing the obtained results with the consequences of the quantitative theory of supramolecular oligomeric structure formation activation mechanism (see Part 2.4.1), let us consider some seemingly contradictory results of the above given experiments, where different methods were used. 

Much biochemical evidence shows that many if not all 7TM receptors have a strong tendency to aggregate both with themselves and with other 7TM receptors, as most clearly seen in multiple high-molecular-weight bands on sodium dodecyl sulfate (SDS) gels. These bands are by no means restricted to dimers as, in most cases, several higher order oligomeric structures are observed. This is an important point to consider when the functional correlation of dimer formation is addressed in non-family C receptors. 

Mani, R., Cady, S.D., Tang, M., Waring, A.J., Lehrer, R.I. and Hong, M. (2006) Membrane-dependent oligomeric structure and pore formation of a beta-hairpin antimicrobial peptide in lipid bilayers from solid-state NMR. Proc. Natl. Acad. Sci. USA 103, 16242-16247. 

II and IV formation, total yield of which equals 50% the rest 50% are represented by oligomeric structures, formed from trans-forms of 1,5-dichlorohexaphenylcyclotetrasiloxane. 

The insulin receptor is the prototype of a tyrosine kinase receptor with a constitutive oligomeric structure. The signalling form is a a.2/ 2 tetramer, but the unit structure is a heterodimer, consisting of a- and P-subunits. But, in contrast to the homo-and heterodimers of other RTK growth factor receptors, the formation of the insulin receptor oligomer is constitutive and not dependent on ligand binding (see Fig. 1.5). 

Fig. 6.4 Receptor-regulated SMADs (R-SMADs) have two homology regions, one at the amino- and one at the cartXM termini, MHl and MH2. They are linked by a proline-rich linker region. The iinker region is highly variable in size and sequence. It participates in the formation of homo-oligomeric structures and contains phosphorylation sites for the MAP kinase. Phosphorylation by the MAP kinase has a negative effect, because it prevents nuclear translocation of the SMADs. R-SMADs interact through the MH2 domain with the activated receptor I and are phosphorylated at the C-terminal SS(V/M)S motif, where S is serine V, valine and M, methionine. Both, MHl and MH2 domains are essential for DNA binding and the recruitment of DNA-binding proteins.

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