Structural basis for the inhibition of insulin-like growth factors by insulin-like growth factor-binding proteins
Structural basis for the inhibition of insulin-like growth factors by insulin-like growth factor-binding proteins
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DOI：
10.1073/pnas.0605652103
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发表时间：
2006-08-29
影响因子：
11.1
通讯作者：
Holak, Tad A.
中科院分区：
文献类型：
--
作者：
Sitar, Tomasz;Popowicz, Grzegorz M.;Holak, Tad A.
胰岛素样生长因子结合蛋白（IGFBP）通过高亲和力的IGFBP/IGF复合物控制胰岛素样生长因子（IGF）1和-2的生物利用度、活性和分布。igf结合位点位于igfbp的两个保守结构域N端和c端片段上。这些结构域对IGFBP/IGF络合的相对贡献一直难以分析，部分原因是缺乏适当的三维结构。为了分析N-和c端结构域相互作用的影响，我们确定了几种x射线结构：首先是IGFBP4和IGF1的N-和c端结构域片段的三元配合物，其次是使用IGFBP1的c端结构域片段而不是IGFBP4的“杂化”三元配合物。我们还求解了IGFBP4和IGF1的n端结构域的二元配合物，再次通过与三元配合物的比较来分析C端和n端结构域的相互作用。这些结构揭示了IGF信号通过IGFBP结合调控的机制。这一发现支持了设计IGFBP变体作为治疗IGF失调疾病的IGF抑制剂的研究。在IGFBP4中，残基1-38形成刚性二硫键阶梯状结构，前5个n端残基与IGF结合并部分掩盖负责1型IGF受体结合的IGF残基。一个高亲和力的igf1结合位点位于残基39和82之间的球状结构中。虽然c端结构域不与IGFBP4的IGH或n端结构域形成稳定的二元配合物，但在三元配合物中，c端结构域与两者都接触，并有助于阻断IGF1的IGF1受体结合区。
Insulin-like growth factor-binding proteins (IGFBPs) control bio-availability, activity, and distribution of insulin-like growth factor (IGF)1 and -2 through high-affinity IGFBP/IGF complexes. IGF-binding sites are found on N- and C-terminal fragments of IGFBPs, the two conserved domains of IGFBPs. The relative contributions of these domains to IGFBP/IGF complexation has been difficult to analyze, in part, because of the lack of appropriate three-dimensional structures. To analyze the effects of N- and C-terminal domain interactions, we determined several x-ray structures: first, of a ternary complex of N- and C-terminal domain fragments of IGFBP4 and IGF1 and second, of a "hybrid" ternary complex using the C-terminal domain fragment of IGFBP1 instead of IGFBP4. We also solved the binary complex of the N-terminal domains of IGFBP4 and IGF1, again to analyze C- and N-terminal domain interactions by comparison with the ternary complexes. The structures reveal the mechanisms of IGF signaling regulation via IGFBP binding. This finding supports research into the design of IGFBP variants as therapeutic IGF inhibitors for diseases of IGF disregulation. In IGFBP4, residues 1-38 form a rigid disulphide bond ladder-like structure, and the first five N-terminal residues bind to IGF and partially mask IGF residues responsible for the type 1 IGF receptor binding. A high-affinity IGF1-binding site is located in a globular structure between residues 39 and 82. Although the C-terminal domains do not form stable binary complexes with either IGH or the N-terminal domain of IGFBP4, in the ternary complex, the C-terminal domain contacts both and contributes to blocking of the IGF1 receptor-binding region of IGF1.