title: The N-terminal subdomain of insulin-like growth factor (IGF) binding protein 6. Structure and interaction with IGFs.
abstract: Insulin-like growth factor binding proteins (IGFBPs) modulate the activity and distribution of insulin-like growth factors (IGFs). IGFBP-6 differs from other IGFBPs in being a relatively specific inhibitor of IGF-II actions. Another distinctive feature of IGFBP-6 is its unique N-terminal disulfide linkages; the N-domains of IGFBPs 1-5 contain six disulfides and share a conserved GCGCC motif, but IGFBP-6 lacks the two adjacent cysteines in this motif, so its first three N-terminal disulfide linkages differ from those of the other IGFBPs. The contributions of the N- and C-domains of IGFBP-6 to its IGF binding properties and their structure-function relationships have been characterized in part, but the structure and function of the distinctive N-terminal subdomain of IGFBP-6 are unknown. Here we report the solution structure of a polypeptide corresponding to residues 1-45 of the N-terminal subdomain of IGFBP-6 (NN-BP-6). The extended structure of the N-terminal subdomain of IGFBP-6 is very different from that of the short two-stranded beta-sheet of the N-terminal subdomain of IGFBP-4 and, by implication, the other IGFBPs. NN-BP-6 contains a potential cation-binding motif; lanthanide ion binding was observed, but no significant interaction was found with physiologically relevant metal ions like calcium or magnesium. However, this subdomain of IGFBP-6 has a higher affinity for IGF-II than IGF-I, suggesting that it may contribute to the marked IGF-II binding preference of IGFBP-6. The extended structure and flexibility of this subdomain of IGFBP-6 could play a role in enhancing the rate of ligand association and thereby be significant in IGF recognition.
authors.affiliation: The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville 3050, Australia.
authors.forename: Indu R
authors.initials: IR
authors.lastname: Chandrashekaran
authors.forename: Shenggen
authors.initials: S
authors.lastname: Yao
authors.forename: Chunxiao C
authors.initials: CC
authors.lastname: Wang
authors.forename: Paramjit S
authors.initials: PS
authors.lastname: Bansal
authors.forename: Paul F
authors.initials: PF
authors.lastname: Alewood
authors.forename: Briony E
authors.initials: BE
authors.lastname: Forbes
authors.forename: John C
authors.initials: JC
authors.lastname: Wallace
authors.forename: Leon A
authors.initials: LA
authors.lastname: Bach
authors.forename: Raymond S
authors.initials: RS
authors.lastname: Norton
mesh_terms: D000595:Amino Acid Sequence; D018976:Insulin-Like Growth Factor Binding Protein 6 / Q000737:chemistry* / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D028581:Lanthanoid Series Elements / Q000378:metabolism; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000138:chemical synthesis; D017434:Protein Structure, Tertiary; D013002:Somatomedins / Q000378:metabolism*
chemical_list: D018976:Insulin-Like Growth Factor Binding Protein 6; D028581:Lanthanoid Series Elements; D010446:Peptide Fragments; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II