Nuclear receptors are transcription factors that bind lipids, an event that induces a structural conformation of the receptor that favors interaction with transcriptional coactivators. The nuclear receptor Steroidogenic Factor-1 (SF-1, NR5A1) binds the signaling phosphoinositides PI(4,5)P2 (PIP2) and PI(3,4,5)P3 (PIP3), and our previous crystal structures showed how the phosphoinositide headgroups regulate SF-1 function. However, what role the acyl chains play in regulating SF-1 structure remains unaddressed. Here, we used X-ray crystallography with in vitro binding and functional assays to examine how the acyl chains of PIP3 regulate human SF-1 ligand-binding domain structure and function. Altering acyl chain length and unsaturation regulates apparent binding of all tested phosphoinositides to SF-1. Mass spectrometry-based lipidomics data suggest C16 and C18 phospholipids preferentially associate with SF-1 expressed ectopically in bacteria. We then solved the 2.5Å crystal structure of SF-1 bound to dioleoyl PIP3(18:1/18:1), to compare it with a matched structure of SF-1 bound to dipalmitoyl PIP3(16:0/16:0). The dioleoyl-bound structure was severely disordered in a specific SF-1 region associated with pathogenic human polymorphisms, and within the coactivator-binding region critical for SF-1 function while inducing increased sensitivity to protease digestion in solution. Validating these structural observations, in vitro functional studies showed dioleoyl PIP3 induced 6-fold poorer affinity of a PGC1α coactivator peptide for SF-1, compared to dipalmitoyl PIP3. Together, these data suggest the chemical nature of the phosphoinositide acyl chains controls the ordered state of specific, clinically important structural regions in SF-1, regulating SF-1 function in vitro.

中文翻译：

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磷酸肌醇 PIP3 的酰基链改变核受体类固醇生成因子 1 (NR5A1) 的结构和功能。


核受体是结合脂质的转录因子，脂质是一种诱导受体结构构象的事件，有利于与转录共激活因子相互作用。核受体类固醇生成因子-1 (SF-1, NR5A1) 结合信号磷酸肌醇 PI(4,5)P2 (PIP2) 和 PI(3,4,5)P3 (PIP3)，我们之前的晶体结构显示了如何磷酸肌醇头基调节 SF-1 功能。然而，酰基链在调节 SF-1 结构中起什么作用仍未得到解决。在这里，我们使用 X 射线晶体学进行体外结合和功能测定，以检查 PIP3 的酰基链如何调节人 SF-1 配体结合域的结构和功能。改变酰基链长度和不饱和度可调节所有测试的磷酸肌醇与 SF-1 的表观结合。基于质谱的脂质组学数据表明，C16 和 C18 磷脂优先与细菌中异位表达的 SF-1 相关。然后，我们解析了与二油酰基 PIP3(18:1/18:1) 结合的 SF-1 的 2.5Å 晶体结构，并将其与与二棕榈酰基 PIP3(16:0/16:0) 结合的 SF-1 的匹配结构进行比较。在与致病性人类多态性相关的特定 SF-1 区域中，以及在对 SF-1 功能至关重要的共激活剂结合区域中，二油酰结合结构严重紊乱，同时诱导对溶液中蛋白酶消化的敏感性增加。为了验证这些结构观察结果，体外功能研究表明，与二棕榈酰 PIP3 相比，二油酰 PIP3 诱导的 PGC1α 共激活肽对 SF-1 的亲和力低 6 倍。总之，这些数据表明磷酸肌醇酰基链的化学性质控制着 SF-1 中特定的、临床上重要的结构区域的有序状态，从而调节 SF-1 的体外功能。