Think about entities that provide flexible –often modular and temporary-
solutions. In the macroscopic world one may envision bamboo or scaffold towers.
There is an interesting group of proteins in cells that support the same
functionality, the
scaffolding proteins.
Scaffs contain protein motifs (eg. SH2,SH3, PDZ domains) that support
specific interactions between proteins as well as Internally Disorganized
Regions (IDRs), flexible protein regions with a role in multiprotein complex
interactivity.
If scaffs link 2 proteins, they are known as 'linkers' or 'adaptors'.
More frequently scaffs provide a scaffold for more than 2 proteins. One of
the emerging structural designs with a specific functional role is the support
of a 3-tier kinase signaling module.
Important regulatory functions include:
1.Degradation: eg. axin binds
phosphorylated β-catenin and facilitates phosphorylation by GSK-3β in the
absence of Wnt signaling activity; As such it promotes degradation. Upon
activation by Wnt-frizzled unphosphorylated catenin may build up in the cytosol
and trigger downstream processes in the nucleus (link)
2.Localization: eg.
One has found that Arf-proteins are expressed and targeted in a cell- and
membrane-specific pattern in kidney epithelial cells gyq6dnu.
3.Clustering:
eg. PSD-95 support multimerization of voltage-activated potassium channels;
likewise ankyrins have been shown to play an important role in transport of ion
channels in cardiac cells. 4.Complex signaling: GTPase proteins from the GIMAP
family, in lymphocytes were demonstrated (Schwefel and Daumke, Small Gtpases.
2011) to link together ("oligomerize") and interact with lipid droplets; This
may allow for a metastable platform for specialized signaling like interaction
with apoptotic bcl proteins. This kind of dynamic membrane scaffolding is part
of current research. Also, in the next section, Ste5 is an example of a MAPK
kinase scaffold that determines the switch-like mating response in yeast...

One of the "must know scaffs" is a scaffold protein that determines the
mating response in yeast. It has been named "STE5". STE refers to 'sterile'
proteins, in which mutations cause deficit signaling of the mating pheromone
(Bardwell, Peptides 2004).
Ste5 is crucial in the mating response as it tethers multiple kinases and
acts as an allosteric kinase activator (PM ID:8062390). The short-cut
explanation is that the phosphorylation state of one of the interaction
partners, Fus3, acts as a switch that determines the fast "2-minutes" mating
response. Once the phosphorylation of Fus3 is complete, it dissociates from ste5
and phosphorylates downstream targets to start the mating response, called
'shmooing'.
http://www.shscaffolding.com/