Signal transducing adaptor proteins (STAPs) are proteins that are accessory to main proteins in a signal transduction pathway.^[1] Adaptor proteins contain a variety of protein-binding modules that link protein-binding partners together and facilitate the creation of larger signaling complexes. These proteins tend to lack any intrinsic enzymatic activity themselves,^[2] instead mediating specific protein–protein interactions that drive the formation of protein complexes. Examples of adaptor proteins include MYD88,^[3][4] Grb2 and SHC1.

Signaling components

Much of the specificity of signal transduction depends on the recruitment of several signalling components such as protein kinases and G-protein GTPases into short-lived active complexes in response to an activating signal such as a growth factor binding to its receptor.

Domains

Adaptor proteins usually contain several domains within their structure (e.g., Src homology 2 (SH2) and SH3 domains) that allow specific interactions with several other specific proteins. SH2 domains recognise specific amino acid sequences within proteins containing phosphotyrosine residues and SH3 domains recognise proline-rich sequences within specific peptide sequence contexts of proteins.

There are many other types of interaction domains found within adaptor and other signalling proteins that allow a rich diversity of specific and coordinated protein–protein interactions to occur within the cell during signal transduction.

Examples of adaptor proteins

Adaptor proteins include:

• BCAR3 – Breast cancer anti-estrogen resistance protein 3
• CBL – Casitas B-lineage Lymphoma
• FRS2 – Fibroblast growth factor receptor substrate 2
• GAB2 – GRB2-associated binding protein 2
• GRAP – GRB2-related adaptor protein
• GRAP2 – GRB2-related adaptor protein 2
• GRB2 – Growth factor receptor-bound protein 2
• IRS1 – Insulin receptor substrate 1
• LDLRAP1 – low-density lipoprotein receptor adaptor protein 1
• MYD88 - Myeloid differentiation primary response gene 88
• NCDN - Neurochondrin
• NCK1 – NCK adaptor protein 1
• NCK2 – NCK adaptor protein 2
• NOS1AP – nitric oxide synthase 1 (neuronal) adaptor protein
• PIK3AP1 – phosphoinositide-3-kinase adaptor protein 1
• SH2B1 – SH2B adaptor protein 1
• SH2B2 – SH2B adaptor protein 2
• SH2B3 – SH2B adaptor protein 3
• SH2D3A -SH2 domain containing 3A
• SH2D3C – SH2 domain containing 3C
• SNTA1 – Syntrophin, alpha 1
• SHB – Src homology 2 domain containing adaptor protein B
• SLC4A1AP – solute carrier family 4 (anion exchanger), member 1, adaptor protein