Difference between Adaptor and Scaffold protein
Both of these types of proteins are involved in the signaling pathway.
Signaling pathway itself is the mechanism, or the process (name it however you like) in which a signal comes to the cell and triggers some ordered series of events (signaling pathway) which results in some changes in the cell. These changes are usually related to the gene expression or solute concentration (solute uptake, e.g.) which allows the cell to respond to the signal and adjust its metabolism to the current conditions in the environment.
Signaling pathway usually starts with the signal itself which binds to the receptor on the cell membrane which then transmits the signal inside through a number of different proteins. Basically, both adaptor and scaffold proteins are “located” in this group of proteins responsible for transmitting the signal from the receptor further down into the cell.
The main difference between them is in their function. They also differ in the structure, of course, but then again this is the case for any two different proteins so it is not worth mentioning. The role of scaffold proteins is to coordinate the signal transduction by “attracting” a number of different proteins needed in the signaling pathway. They basically form a complex of proteins by tethering other actors in the pathway, thus localizing them to a specific place, making the signal transduction more effective. Having this role, they can also regulate the signaling pathway (through positive and negative feedback signals) and they can isolate specific proteins (the right ones needed in the current active pathway) from other competitive proteins that are not wanted during that time.
Adaptor proteins, on the other hand, are smaller and they too help in the formation of protein complexes, but they do so by usually binding only two proteins. They accomplish this through specific domains (usually SH2 and SH3) which recognize specific amino acid sequences in the target protein.
One of the best examples for scaffold protein is MEKK1, which is present in the MAPK pathway (mitogen-activated protein kinase). This pathway is responsible for sending the signal further into the nucleus, regulating specific transcription factors responsible for the expression of proteins which affect the cell-cycle and cell differentiation.
Good example of adaptor protein is GRB2 (growth factor receptor-bound protein 2). It sends the signal further down by binding to the EGF receptor (epidermal growth factor receptor) with SH2 domain, and it attracts the next protein in the pathway (Sos protein in this case) with SH3 domains.
Hope this answers your question. Sorry if I have made the answer too long, but I like to start from the beginning, just in case if somebody else is searching for this, but lacks the basic knowledge needed to understand the subject.
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