Structure And Function Of LGN Conformation Regulation Of Asymmetric Cleavage - Related Proteins In Cells

Stem cells are unique in their ability to self-renew and to produce daughter cells committed to differentiation. Many stem cells can divide symmetrically, particularly when they are expanding in number during development or after injury. In asymmetric cell divisions, all cell fate detaminatants are distributed into only one daughter cell, so the two daughter cells have different fate, one of which remains the characteristic of stem cell like her mother, whereas the other one of which differentiates. According the preview research results, we know that asymmetric cell division is an important and conserved strategy in the generation of cellular diversity during animal development. It is of vital importance for stem cells to tightly control this switch between symmetric divisions and asymmetric divisions during tissue repair and development because, if that homeostasis is not maintained, premature differentiation may lead to incomplete tissue or organ development, whereas excessive cell proliferation act as a main reason for tumour formation.At present, it is widely accepted that asymmetric divisions are regulated by intrisic mechanism and extrinsic mechanism. Extrinsic cues, extrinsic signal and all extrinsic surrounding of stem cells play a key role of cell fate decision, witch is called extrinsic mechanism of asymmetric cell divisions. In the intrisic mechanism, the regulation mostly depends on many protein complex within cell, such as Par-6/Par-3/aPKC, Pins/Dig, Pins/NuMA, Numb/PTB and so on. The study about these complex have made great progress in recent years, but the protein structures and details of regulation mechanism in this field remian unclear.In previous years, Prehoda’s and Du Quansheng’s team have done lots of work on a very important protein named LGN in asymmetric cell divisions, of which the N terminal TPR domain interact with which C terminal GoLoco domain.. The intramolecular self-interaction of LGN is regulated by interacting with NuMA and Gai respectively or simultaneously, so that LGN function as a conformation switch.In this dissertation, I focuses on the mechanism of LGN autoinhibiton.We work very hard to obtain the structure of TPR/GoLoco and realize the binding details between TPR domian and GoLoco domain by NMR, protein crystal and biochemical assays. Furthermore, we find all the four GoLoco motifs bind to TPR domian, which is different with the Pins.Comparison of the structure of NuMA/TPR and the stucture of TPR/GoLoco opens up the overlap region of NuMA binding sites and GoLoco binding sites on TPR domain, which is comfirmed by other biochemical assays. Then, we find out that the NuMA and Gai mutually enhance the binding with the Pins FL by protein binding assays. Our data make clear the "semi-open" conformation of Pins when only associated with NuMA and the "full open" conformation of Pins binding with both NuMA and Gai. All information we provide is very important for researchers to go deep into this feld.In the forth chapter, the main content focuses on the similarities between interaction of NuMA/TPR and the interaction of Frmpdl/TPR by crystal structure and binding assays. Because of the similarities, we suppose that Frmpdl and NuMA may play some parallel role in the cell polarity and asymmetric divisions.