Oligomerization of proteins in the plasma membrane has been postulated as a regulatory principle following the well-known example of oligomeriza-tion of mammalian receptor tyrosine kinases depending on tissue or ligand (Olayioye et al. 2000). In plants, oligomerization of transporters has been suggested to be a key process during regulation of sucrose transport (Barker et al. 2000; Reinders et al. 2002), and oligomerization of receptor kinases is discussed today as a general principle in plant signaling ranging from hormone signaling pathways to pathogen signaling. The oligomeric interaction between the receptor kinase BRI1 and the receptor kinase BAK1, as well as the endocytotic recycling of this signaling complex, is one of the first examples of a regulatory role of membrane protein oligomerization in plants (Russinova et al. 2004).
For the analysis of the oligomeric nature of protein complexes, blue native gel electrophoresis is very powerful (Eubel et al. 2005). Especially in the plant field, it has successfully been used to characterize the composition of the plant mitochondrial respiratory chain (Eubel et al. 2004) and, in combination with protein mass spectrometry, the composition of the plant photosystem was elucidated (Heinemeyer et al. 2004). In a systematic large-scale approach the oligomeric state of all stromal chloroplast proteins was characterized using blue native gel and subsequent protein identification by mass spectrometry (Peltier et al. 2006).
In future, and in combination with powerful stable isotope labeling techniques (Engelsberger et al. 2006), blue native gels and LC/MS/MS analysis will have high potential for the analysis of changes in oligomerization state upon external or internal stimulation. The analysis of signaling cascades may then become even more complex.
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