IQGAP1 - Function As A Scaffold

Function As A Scaffold

Protein binding does not by itself construct an interesting story. Far more important is the outcome of the binding event. Does binding change the target protein’s localization? Does it activate the target, or in some way change the target (or effector molecule’s) conformation? As a scaffolding protein, IQGAP1 binds and regulates many targets—its role is to integrate and mediate signaling from diverse pathways and insulate key pathway members from crosstalk.

Scaffolds organize signaling pathways—help regulate how various extracellular signals can be transduced by the same canonical pathway members into various cellular outputs. Generally, scaffolds regulate output, localization, and selectivity of pathways.

As a scaffold involved in different signaling pathways (actin cytoskeleton, cellular adhesion, cell cycle, transcription), IQGAP1 has a unique ability to potentially couple diverse cellular functions. For example IQGAP1 is associated with actin dynamics through direct binding of actin and indirect regulation via Cdc42/Rac1, but also modulates the MAPK pathway which is associated with cell cycle control. Thus IQGAP1 may couple MAPK signaling (decisions about cell fate) to the cytoskeleton or cellular adhesion (potentially acting out those decisions)—an important implication for cancer.

To simplify, due to its diverse range of binding partners, IQGAP1 may act as a link between logically related but molecularly distinct cellular functions. In the above example, actin cytoskeleton rearrangement is required for proliferation (cytokinesis during mitosis). IQGAP1 helps cells both listen to and act on signals, playing an integral role in connecting the dots between signals for proliferation and the actual cellular response.