Insulin-like growth factor-binding protein

The insulin-like growth factor-binding protein (IGFBP) serves as a transport protein for insulin-like growth factor 1 (IGF-1).^[2]

Insulin-like growth factor binding protein
Structure of the IGF-binding domain of the insulin-like growth factor-binding protein-5 (IGFBP-5)[1]
Identifiers
Symbol	IGFBP
Pfam	PF00219
InterPro	IPR000867
SMART	SM00121
PROSITE	PDOC00194
SCOP2	1boe / SCOPe / SUPFAM
Available protein structures: Pfam   structures / ECOD   PDB RCSB PDB; PDBe; PDBj PDBsum structure summary PDB 1boe​, 1h59​

Function

Approximately 98% of IGF-1 is always bound to one of six binding proteins (IGF-BP). IGFBP-3, the most abundant protein, accounts for 80% of all IGF binding. IGF-1 binds to IGFBP-3 in a 1:1 molar ratio. IGF-BP also binds to IGF-1 inside the liver, allowing growth hormone to continuously act upon the liver to produce more IGF-1.

IGF binding proteins (IGFBPs) are proteins of 24 to 45 kDa. 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.

Family members

In humans, IGFBPs are transcribed from the following seven genes:

• IGFBP1
• IGFBP2
• IGFBP3
• IGFBP4
• IGFBP5
• IGFBP6
• IGFBP7

See also

• Insulin-like growth factor receptor