C-terminal domain of insulin-like growth factor (IGF) binding protein 6: Conformational exchange and its correlation with IGF-II binding

Yao, SG; Headey, SJ; Keizer, DW; Bach, LA; Norton, RS

Author(s): Yao, SG; Headey, SJ; Keizer, DW; Bach, LA; Norton, RS;
Details: Publication Year 2004-09-07,Volume 43,Issue #35,Page 11187-11195
Journal Title: BIOCHEMISTRY
Publication Type: Journal Article
Abstract: Insulin-like growth factor binding proteins (IGFBPs) function as carriers and regulators of the insulin-like growth factors (IGF-I and -II). Within the family of six binding proteins, IGFBP-6 is unique in having a 20-100-fold higher affinity for IGF-II over IGF-I and appears to act primarily as an inhibitor of IGF-II actions. We have recently determined the solution structure of the C-terminal domain of IGFBP-6 (C-BP-6), which shows the presence of substantial flexible regions, including three loop regions. In this paper, we report results from N-15 relaxation measurements carried out in both the laboratory and rotating frames. Analysis of conventional N-15 relaxation data (R-1, R-2, and steady-state N-15-{H-1} nuclear Overhauser effect) indicated that there was a considerable number of residues involved in conformational/cheMical exchange. Measurements of off-resonance N-15 R-1p in the rotating frame and N-15 relaxation dispersion using an in- and antiphase coherence-averaged Carr- Purcell -Meiboom- Gill sequence were thus carried out to gain further insight into the solution dynamics of C-BP-6. Although the off-resonance N-15 relaxation data showed no clear evidence for residues undergoing microsecond motion, the N-15 relaxation dispersion data allowed us to identify 15 residues that clearly exhibit submilli- to millisecond motion. A good correlation was observed between residues exhibiting motion at submilli- to millisecond time scales and those affected by IGF-II binding, as identified through the perturbation of nuclear magnetic resonance (NMR) spectra of C-BP-6 following IGF-II addition. A complete NMR relaxation study of C-BP-6 dynamics in complex with IGF-II was hampered by peak broadening and disappearance of C-BP-6 in the presence of IGF-II. Nonetheless, current results strongly suggest possible conformation switching or population shifting between pre-existing conformations in C-BP-6 upon binding to IGF-II.
Publisher: AMER CHEMICAL SOC
Keywords: N-15 NMR RELAXATION; TIME-SCALE DYNAMICS; BACKBONE DYNAMICS; CHEMICAL-EXCHANGE; ROTATIONAL DIFFUSION; HETERONUCLEAR NMR; PROTEIN-5 IGFBP-5; SLOW MOTIONS; SPECTROSCOPY; INHIBITOR
Publisher's Version: https://doi.org/10.1021/bi049456+
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Creation Date: 2004-09-07 12:00:00