third type I K homology (KH) RNA-binding domain found in insulin-like growth factor 2 mRNA-binding protein 3 (IGF2BP3) and similar proteins
IGF2BP3, also called IGF2 mRNA-binding protein 3 (IMP-3), or hepatocellular carcinoma autoantigen p62, or IGF-II mRNA-binding protein 3, or VICKZ family member 3 (VICKZ3), or KH domain-containing protein overexpressed in cancer, or KOC, is primarily found in the nucleolus, where it can bind to the 5' UTR of the insulin-like growth factor II leader 3 mRNA and may repress translation of insulin-like growth factor II during late development. It acts as an RNA-binding factor that may recruit target transcripts to cytoplasmic protein-RNA complexes (mRNPs). It also modulates the rate and location at which target transcripts encounter the translational apparatus and shields them from endonuclease attacks or microRNA-mediated degradation. IGF2BP3 binds to the 3'-UTR of CD44 mRNA and stabilizes it, hence promotes cell adhesion and invadopodia formation in cancer cells. It also binds to beta-actin/ACTB and MYC transcripts. IGF2BP3 can form homooligomers and heterooligomers with IGF2BP1 and IGF2BP2 in an RNA-dependent manner. IGF2BP3 contains four K-homology (KH) RNA-binding domains which are important in RNA binding and are known to be involved in RNA synthesis and metabolism. The model corresponds to the third one.
Comment:Essential to the KH domain, the RNA-binding platform is a strictly conserved GXXG motif, located within a flexible loop between alpha1 and alpha2. This GXXG motif, in concert with a variable loop located between beta2 and beta', functions to clamp an RNA substrate in place upon binding.