Vitamin A is a necessary nutrient for all mammals, and it is required for the transcription of many genes and vital for vision. While fasting, the vitamin A alcohol form (Retinol) from storage in the liver is mobilized and transported through the bloodstream while bound to retinol binding protein (RBP). Details of how exactly vitamin A is released from RBP and taken into the cells are still unclear. As part of the effort to elucidate the specifics of this process, single-particle cryo-electron microscopy structural studies of STRA6 (the RBP receptor 75-kDa transmembrane receptor protein) were recently reported by Chen et al. (Science, https://doi.org/10.1126/science.aad8266, 2016). Interestingly, STRA6 from zebrafish was shown to be a stable dimer and bound to calmodulin (CaM), forming a 180-kDa complex. The topology of the STRA6 complex includes 18 transmembrane helices (nine per protomer) and two long horizontal intramembrane helices interacting at the dimer core (Chen et al., in Science, https://doi.org/10.1126/science.aad8266, 2016). CaM was shown to interact with three regions of STRA6, termed CaMBP1, CaMBP2, and CaMBP3, with the most extensive interactions involving CaMBP2. To further our understanding of Ca²⁺-dependence of CaM-STRA6 complex formation, studies of the structure and dynamic properties of the CaMBP2–CaM complex were initiated. For this, the¹H^{N, 13}C, and¹⁵N backbone resonance assignments of the 148 amino acid Ca²⁺-bound calmodulin protein bound to the 27-residue CaMBP2 peptide derived from STRA6 were completed here using heteronuclear multidimensional NMR spectroscopy.

中文翻译：

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人钙调蛋白的1HN，13C和15N共振分配与衍生自STRA6维生素A转运蛋白（CaMBP2）的肽结合。

维生素A是所有哺乳动物的必需营养素，它是许多基因转录所必需的，并且对视力至关重要。禁食时，肝脏中储存的维生素A醇形式（视黄醇）可动员并通过血流转运，并与视黄醇结合蛋白（RBP）结合。维生素A如何从RBP释放并进入细胞的细节仍不清楚。作为阐明这一过程细节的努力的一部分，Chen等人最近报道了STRA6（RBP受体75-kDa跨膜受体蛋白）的单粒子低温电子显微镜结构研究。（科学，https：//doi.org/10.1126/science.aad8266,2016）。有趣的是，斑马鱼的STRA6被证明是稳定的二聚体，并与钙调蛋白（CaM）结合，形成一个180 kDa的复合物。STRA6复合体的拓扑结构包括18个跨膜螺旋（每个原发组织为9个）和两个较长的水平膜内螺旋在二聚体核心处相互作用（Chen等，in Science，https://doi.org/10.1126/science.aad8266，2016） ）。显示出CaM与STRA6的三个区域相互作用，称为CaMBP1，CaMBP2和CaMBP3，其中涉及CaMBP2的相互作用最为广泛。进一步了解CaCaM-STRA6复合物的形成具有²⁺依赖性，因此开始了对CaMBP2-CaM复合物的结构和动力学性质的研究。为此，在此使用异核多维NMR谱图完成了与源自STRA6的27个残基CaMBP2肽结合的148个氨基酸的Ca ²⁺结合的钙调蛋白蛋白的¹ H ^N，13 C和¹⁵ N骨架共振分配。