Insulin Binding: Receptors, Dimers, Hexamers, and Other Interactions

Insulin primarily binds to the insulin receptor (INSR), which is a tyrosine kinase receptor. However, insulin also has some affinity for the insulin-like growth factor 1 receptor (IGF1R), although it binds with much lower affinity compared to its binding to INSR.

On the other hand, insulin does not bind to the insulin-like growth factor 2 receptor (IGF2R) significantly. IGF2R primarily binds to IGF2 and acts as a clearance receptor for this growth factor.

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

Insulin can also form hexamers in the presence of zinc ions. These hexamers are the storage form of insulin in the pancreas and are released into the bloodstream as needed. However, once in the bloodstream, insulin typically exists as a monomer.

In addition to its interactions with receptors and self-association, insulin can also bind to other molecules. For example, insulin can bind to insulin-like growth factor-binding proteins (IGFBPs) that regulate its availability and activity. Insulin can also interact with insulin-degrading enzyme (IDE), which plays a role in its degradation and clearance from the body.