The SCHOOL of nature: II. Protein order, disorder and oligomericity in transmembrane signaling.

Recent reports have revealed that many proteins that do not adopt globular structures under native conditions, thus termed intrinsically disordered proteins (IDPs), are involved in cell signaling. Intriguingly, physiologically relevant oligomerization of IDPs has been recently observed and shown to exhibit unique biophysical characteristics, including the lack of significant changes in chemical shift and peak intensity upon binding. In this work, I summarize several distinct features of protein disorder that are especially important as related to receptor-mediated transmembrane signal transduction. I also hypothesize that interactions of IDPs with their protein or lipid partners represent a general biphasic process with the "no disorder-to-order" fast interaction which, depending on the interacting partner, may or may not be accompanied by the slow formation of a secondary structure. Further, I suggest signaling-related functional connections between protein order, disorder, and oligomericity and hypothesize that receptor oligomerization induced or tuned upon ligand binding outside the cell is translated across the membrane into protein oligomerization inside the cell, thus providing a general platform, the Signaling Chain HOmoOLigomerization (SCHOOL) platform, for receptor-mediated signaling. This structures our current multidisciplinary knowledge and views of the mechanisms governing the coupling of recognition to signal transduction and cell response. Importantly, this approach not only reveals previously unrecognized striking similarities in the basic mechanistic principles of function of numerous functionally diverse and unrelated surface membrane receptors, but also suggests the similarity between therapeutic targets, thus opening new horizons for both fundamental and clinically relevant studies.