Recommendations for nomenclature of the insulin-like growth factor binding protein superfamily

THE NOMENCLATURE for the insulin-like growth factor (IGF) binding proteins (IGFBP) was established at the 2nd and 3rd International IGF Symposia. The IGFBPs constitute a family of six structurally related proteins that bind IGF peptides with high affinity (typical Kd in the 10−10 to 10−11m range). They share an overall protein sequence identity of approximately 50% and contain 16–18 conserved cysteines in the NH2- and COOH-terminal regions. Recently, the predicted protein product of the mac25 complementary DNA was shown to be structurally related to the IGFBPs, especially in the amino-terminal region, where 11–12 of the 12 cysteines found in IGFBPs 1–6 are conserved. The protein was synthesized in a baculovirus expression system, found to be identical to previously described tumor-derived adhesion factor and prostacyclin-stimulating factor, and to bind IGF-I, IGF-II, and insulin, but with relatively low affinity. It was, accordingly, provisionally named IGFBP-7.