Receptor structure and inhibition of midkine, a growth factor controled by retinoic acid

我们研究了midkine （MK）的结构和功能。化学合成的MK c端半分子具有促进神经突生长活性和肝素结合活性。一个突变的MK，其假定的肝素结合位点被体外诱变改变，失去了促进神经突的活性，表明肝素结合活性与促进神经突的活性相关。通过化学修饰的肝素和肝素衍生的寡糖分析了与MK结合的结构要求。所有的硫酸盐基团（2-0,6-0,2- n）都是抑制神经突促进活性所必需的。抑制所需的肝素寡糖的大小约为20mer。另一方面，通过分析与MK柱结合的膜蛋白，揭示了一个假定的MK受体。建立了一种定位蛋白性质MK受体的组织化学方法。我们还获得了MK表达与癌症、脑梗死、心梗和类风湿关节炎相关的结果。还设计了一种灵敏的测定MK水平的方法，使血清样品中的MK检测成为可能。

We studied on structure and function of midkine (MK). Chemically synthesized C-terminal half molecule of MK has neurite outgrowth promoting activity and heparin binding activity. A mutant MK whose putative heparin binding sites were altered by in vitro mutagenesis lost neurite promoting activity, indicating that heparing binding activity correlates with neurite promoting activity. Structural requirements for binding to MK was analyzed by chemically modified heparing and heparin-derived oligosaccharides. All of sulfate groups (2-0,6-0,2-N) were required for inhibition of neurite promoting activity. The size of heparin oligosaccharide necessary for the inhibition was about 20-mer. On the other hand, a putative MK receptor was disclosed by analysis of membrane proteins binding to MK column. A histochemical method to localize the MK receptor of protein nature was also established. We also obtained results indicating the correlation of MK expression and cancer, brain and heart infarction and rheumatoid arthritis. A sensitive method to determine MK levels was also devised, enabling MK assay in serum samples.