Unit for Structural Biology, Department of Biochemistry and Microbiology, Ghent University, Technologiepark-Zwijnaarde 71, 9052 Zwijnaarde, Belgium.
Acta Crystallogr F Struct Biol Commun. 2021 Apr 1;77(Pt 4):121-127. doi: 10.1107/S2053230X21003289. Epub 2021 Apr 6.
The overarching paradigm for the activation of class III and V receptor tyrosine kinases (RTKs) prescribes cytokine-mediated dimerization of the receptor ectodomains and homotypic receptor-receptor interactions. However, structural studies have shown that the hematopoietic receptor FLT3, a class III RTK, does not appear to engage in such receptor-receptor contacts, despite its efficient dimerization by dimeric FLT3 ligand (FL). As part of efforts to better understand the intricacies of FLT3 activation, we sought to engineer a monomeric FL. It was found that a Leu27Asp substitution at the dimer interface of the cytokine led to a stable monomeric cytokine (FL) without abrogation of receptor binding. The crystal structure of FL at 1.65 Å resolution revealed that the introduced point mutation led to shielding of the hydrophobic footprint of the dimerization interface in wild-type FL without affecting the conformation of the FLT3 binding site. Thus, FL can serve as a monomeric FL variant to further interrogate the assembly mechanism of extracellular complexes of FLT3 in physiology and disease.
III 类和 V 类受体酪氨酸激酶（RTKs）的激活的总体模式规定了细胞因子介导的受体胞外结构域二聚化和同型受体-受体相互作用。然而，结构研究表明，造血受体 FLT3 是一种 III 类 RTK，尽管其通过二聚体 FLT3 配体（FL）有效二聚化，但似乎不参与这种受体-受体接触。作为更好地理解 FLT3 激活复杂性的努力的一部分，我们试图设计一种单体 FL。研究发现，细胞因子二聚体界面处的 Leu27Asp 取代导致稳定的单体细胞因子（FL），而不会阻断受体结合。1.65 Å分辨率的 FL 晶体结构显示，引入的点突变导致在不影响 FLT3 结合位点构象的情况下，对野生型 FL 中二聚化界面的疏水性足迹进行屏蔽。因此，FL 可以作为单体 FL 变体，以进一步研究生理和疾病中 FLT3 细胞外复合物的组装机制。
