Department of Pediatrics, University of Western Ontario, Ontario, Canada.
J Proteome Res. 2010 Apr 5;9(4):1873-81. doi: 10.1021/pr900987n.
Phosphorylation enhances IGFBP-1 binding to IGF-I, thereby limiting the bioavailability of IGF-I that may be important in fetal growth. Our goal in this study was to determine whether changes in site-specific IGFBP-1 phosphorylation were unique to fetal growth restriction. To establish a link, we compared IGFBP-1 phosphorylation (sites and degree) in amniotic fluid from FGR (N = 10) and controls (N = 12). The concentration of serine phosphorylated IGFBP-1 showed a negative correlation with birth weight in FGR (P = 0.049). LC-MS/MS analysis revealed all four previously identified phosphorylation sites (Ser98, Ser101, Ser119, and Ser169) to be common to FGR and control groups. Relative phosphopeptide intensities (LC-MS) between FGR and controls demonstrated 4-fold higher intensity for Ser101 (P = 0.026), 7-fold for Ser98/Ser101 (P = 0.02), and 23-fold for Ser169 (P = 0.002) in the FGR group. Preliminary BIAcore data revealed 4-fold higher association and 1.7-fold lower dissociation constants for IGFBP-1/IGF-I in FGR. A structural model of IGFBP-1 bound to IGF-I indicates that all the phosphorylation sites are on relatively mobile regions of the IGFBP-1 sequence. Residues Ser98, Ser101, and Ser169 are close to structured regions that are involved in IGF-I binding and, therefore, could potentially make direct contact with IGF-I. On the other hand, residue Ser119 is in the middle of the unstructured linker that connects the N- and C-terminal domains of IGFBP-1. The model is consistent with the assumption that residues Ser98, Ser101, and Ser169 could directly interact with IGF-I, and therefore phosphorylation at these sites could change IGF-I interactions. We suggest that site-specific increase in IGFBP-1 phosphorylation limits IGF-I bioavailability, which directly contributes to the development of FGR. This study delineates the potential role of higher phosphorylation of IGFBP-1 in FGR and provides the basis to substantiate these findings with larger sample size.
磷酸化增强 IGFBP-1 与 IGF-I 的结合，从而限制 IGF-I 的生物利用度，这在胎儿生长中可能很重要。我们在这项研究中的目标是确定 IGFBP-1 磷酸化的特定部位的变化是否仅与胎儿生长受限有关。为了建立联系，我们比较了来自胎儿生长受限（FGR）（N=10）和对照组（N=12）的羊水 IGFBP-1 磷酸化（部位和程度）。FGR 中丝氨酸磷酸化 IGFBP-1 浓度与出生体重呈负相关（P=0.049）。LC-MS/MS 分析显示，所有四个先前确定的磷酸化位点（Ser98、Ser101、Ser119 和 Ser169）在 FGR 和对照组中均为常见。FGR 和对照组之间的相对磷酸肽强度（LC-MS）显示，FGR 组中 Ser101 的强度高 4 倍（P=0.026），Ser98/Ser101 的强度高 7 倍（P=0.02），Ser169 的强度高 23 倍（P=0.002）。初步 BIAcore 数据显示，FGR 中 IGFBP-1/IGF-I 的结合常数高 4 倍，解离常数低 1.7 倍。IGFBP-1 与 IGF-I 结合的结构模型表明，所有磷酸化位点都位于 IGFBP-1 序列中相对移动的区域。残基 Ser98、Ser101 和 Ser169 靠近涉及 IGF-I 结合的结构区域，因此可能与 IGF-I 直接接触。另一方面，残基 Ser119 位于连接 IGFBP-1 N 端和 C 端结构域的无规卷曲连接物的中间。该模型与假设一致，即残基 Ser98、Ser101 和 Ser169 可以直接与 IGF-I 相互作用，因此这些位点的磷酸化可以改变 IGF-I 的相互作用。我们认为 IGFBP-1 磷酸化的特定部位增加会限制 IGF-I 的生物利用度，这直接导致 FGR 的发生。本研究阐述了 IGFBP-1 磷酸化程度增加在 FGR 中的潜在作用，并为使用更大的样本量证实这些发现提供了基础。
