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The O-glycosylation sites, carbohydrate structure and disulfide linkages of human insulin-like growth factor binding protein 6 were investigated. Electrospray ionization mass spectrometry was used along with Edman N-terminal amino acid sequencing of intact glycoprotein and tryptic fragments purified by microbore high-performance liquid chromatography. Results showed that two disulfide-linked subdomains exist within each of the N- and C-terminal regions, indicating that the latter regions are unrelated.

The cross-linking and nuclear magnetic resonance (NMR) spectroscopy was used to study the molecular interactions among the N-domain of insulin-like growth factor-binding protein-2 (IGFBP-2) (N-BP-2), C-BP-2, and IGFs. The results reveal that low molecular weight heparin bound to the IGF-I*N-BP-2*C-BP-2 ternary complex but did not cause it to dissociate.

The solution structure of a polypeptide corresponding to the residues of the N-terminal subdomain of insulin-like growth factor binding protein 6 (IGGBP-6) (NN-BP-6) is presented. The extended structure and flexibility of the subdomain of IGFBP-6 has played a major role in enhancing the rate of ligand association and hence is important in insulin-like growth factor (IGF) recognition.

The results from (super 15)N relaxation measurements carried out in both the laboratory and frames for the insulin-like growth factors binding proteins (IGFBPs) are presented. The results strongly suggest possible conformation switching or population shifting between pre-existing conformations in C-terminal domain of IGFBP-6 upon binding to insulin-like growth factors (IGF)-II.