All six IGFBPs share 50% homology with each other and have binding affinities for IGF-I and IGF-II at the same order of magnitude as the ligands have for the IGF-IR.

[3] The IGFBPs help to lengthen the half-life of circulating IGFs in all tissues, including the prostate.

[4] Individual IGFBPs may act to enhance or attenuate IGF signaling depending on their physiological context (i.e. cell type).

Even with these similarities, some characteristics are different: chromosomal location, heparin binding domains, RGD recognition site, preference for binding IGF-I or IGF-II, and glycosylation and phosphorylation differences.

[5] These structural differences can have a tremendous impact on how the IGFBPs interact with cellular basement membranes.