Crystallographic Studies Of Necl-1 Ig-like V Domain

The research on three-dimentional structure of proteins becomes an important mission to decode the life at the age of post-gonomics. A comment in science noted: it is crucial to elucidate the relationship between the function and the structure of proteins. In cooperation with Prof. Rao's lab in Tsinghua University, we conducted the study on structures of some neuronal related proteins on the basis of their functional research.Nectins and necls are Ca²⁺-independent Ig-like cell adhesion molecules that play roles in organization of a variety of cell-cell junctions. All members have three Ig-like loops in the extracellular region. The first is essential for the trans-dimer formation of nectin of two neighboring cells, causing cell-cell adhesion. Tissue distribution analysis showed that Necl-1 was specifically expressed in the neural tissue. It localizes at the contact sites between two axon terminals, between an axon terminal and an axonal shaft, and between an axon terminal and glia cell processes in cerebellum. Necl-1 shows Ca²⁺-independent homo- and heterophilic cell-cell adhesion activity with Necl-2, nectin-1, and nectin-3.In this thesis, necl-1 Ig V domain was crystallized with high quality. It can diffract to 2.0 A and belongs to the space group C222₁. Furthermore, the Se-Met crystal was also obtained and the crystal structure of necl-1 Ig V domain was determined by Multiple-wavelength Anomalous Diffraction (MAD) method. Two molecules are present in the asymmetric unit of the crystal (designated A, B), and they are associated to form dimmer. The structure has most of the features of the variable (V)-set of the Ig superfamily of structures. The surface area buried upon dimer formation was 1405 A. The dimmer was maintained by hydrophobic interaction and hydrogen bonds. Previous studies indicate that Nectins have similar structure to Necls, thus, the structure of the first Ig-like domain offers a framework for predicting the oligomeric state of other Necls and Nectins. Furthermore, we also analyzed the biochemical and biophysical characterizations of necl-1 Ig V domain in this thesis.Meanwhile, three other ptroteins DPY-30 -like, SNCA and SNCG were expressed, purified and crystallized. Good crystals suitable for diffraction were obtained. The...