Insulin Binding: Receptor Interactions, Dimerization, and Other Molecules

Insulin primarily binds to the insulin receptor (IR) located on the surface of target cells. However, insulin can also bind to the insulin-like growth factor 1 receptor (IGF1R), although with much lower affinity compared to its binding to the IR. This cross-binding between insulin and IGF1R allows for some overlapping biological effects between insulin and insulin-like growth factors (IGFs).

Insulin does not bind to the insulin-like growth factor 2 receptor (IGF2R), as this receptor specifically binds to IGF2 and not insulin.

Insulin can form dimers, which is the association of two insulin molecules together. This dimerization is important for insulin's binding to the insulin receptor and subsequent activation of signaling pathways.

Under certain conditions, insulin can also form hexamers, where six insulin molecules associate together. This hexameric form of insulin is commonly found in storage granules within pancreatic beta cells and serves as a reservoir for insulin secretion. However, when insulin needs to be released into the bloodstream, it is typically in its monomeric form.

Insulin can also bind to other molecules, such as insulin-like growth factors (IGFs), insulin-like growth factor binding proteins (IGFBPs), and insulin-degrading enzyme (IDE). These interactions play roles in regulating insulin's activity, transportation, and degradation within the body.