The guanine-nucleotide exchange factor (GEF) RalGPS1a activates small GTPase Ral proteins such as RalA and RalB by stimulating the exchange of Ral bound GDP to GTP, thus regulating various downstream cellular processes. RalGPS1a is composed of an Nterminal Cdc25-like catalytic domain, followed by a PXXP motif and a C-terminal pleckstrin homology (PH) domain. The Cdc25 domain of RalGPS1a, which shares about 30% sequence identity with other Cdc25-domain proteins, is thought to be directly engaged in binding and activating the substrate Ral protein. Here we report the crystal structure of the Cdc25 domain of RalGPS1a. The bowl shaped structure is homologous to the Cdc25 domains of SOS and RasGRF1. The most remarkable difference between these three Cdc25 domains lies in their active sites, referred to as the helical hairpin region. Consistent with previous enzymological studies, the helical hairpin of RalGPS1a adopts a conformation favorable for substrate binding. A modeled RalGPS1a-RalA complex structure reveals an extensive binding surface similar to that of the SOS-Ras complex. However, analysis of the electrostatic surface potential suggests an interaction mode between the RalGPS1a active site helical hairpin and the switch 1 region of substrate RalA distinct from that of the SOS-Ras complex.
Amino Acid Sequence ; Binding Sites ; Catalytic Domain ; Cloning, Molecular ; Crystallography, X-Ray ; Escherichia coli ; Guanosine Diphosphate ; metabolism ; Guanosine Triphosphate ; metabolism ; Humans ; Models, Molecular ; Molecular Conformation ; Molecular Sequence Data ; Plasmids ; metabolism ; Protein Binding ; Protein Structure, Tertiary ; genetics ; Recombinant Proteins ; chemistry ; genetics ; metabolism ; ral GTP-Binding Proteins ; chemistry ; genetics ; metabolism ; ral Guanine Nucleotide Exchange Factor ; chemistry ; genetics ; metabolism

Human noroviruses (huNoVs) recognize histo-blood group antigens (HBGAs) as attachment factors, in which genogroup (G) I and GII huNoVs use distinct binding interfaces. The genetic and evolutionary relationships of GII huNoVs under selection by the host HBGAs have been well elucidated via a number of structural studies; however, such relationships among GI NoVs remain less clear due to the fact that the structures of HBGA-binding interfaces of only three GI NoVs with similar binding profiles are known. In this study the crystal structures of the P dimers of a Lewis-binding strain, the GI.8 Boxer virus (BV) that does not bind the A and H antigens, in complex with the Lewis b (Le(b)) and Le(y) antigens, respectively, were determined and compared with those of the three previously known GI huNoVs, i.e. GI.1 Norwalk virus (NV), GI.2 FUV258 (FUV) and GI.7 TCH060 (TCH) that bind the A/H/Le antigens. The HBGA binding interface of BV is composed of a conserved central binding pocket (CBP) that interacts with the β-galactose of the precursor, and a well-developed Le epitope-binding site formed by five amino acids, including three consecutive residues from the long P-loop and one from the S-loop of the P1 subdomain, a feature that was not seen in the other GI NoVs. On the other hand, the H epitope/acetamido binding site observed in the other GI NoVs is greatly degenerated in BV. These data explain the evolutionary path of GI NoVs selected by the polymorphic human HBGAs. While the CBP is conserved, the regions surrounding the CBP are flexible, providing freedom for changes. The loss or degeneration of the H epitope/acetamido binding site and the reinforcement of the Le binding site of the GI.8 BV is a typical example of such change selected by the host Lewis epitope.
Binding Sites ; Blood Group Antigens ; chemistry ; immunology ; Caliciviridae Infections ; immunology ; virology ; Crystallography, X-Ray ; Epitopes ; chemistry ; immunology ; Evolution, Molecular ; Humans ; Lewis Blood-Group System ; chemistry ; immunology ; Norovirus ; chemistry ; immunology ; pathogenicity ; Protein Binding ; Viral Proteins ; chemistry ; immunology

Tongxie Yaofang， also known as Baizhu Shaoyaosan， was first recorded in Danxi's Experiential Therapy （《丹溪心法》） by ZHU Danxi in the Yuan dynasty. It is composed of Atractylodis Macrocephalae Rhizoma， Paeoniae Radix Alba， Citri Reticulatae Pericarpium， and Saposhnikoviae Radix， and serves as the representative prescription for the treatment of painful diarrhea. It has the functions of tonifying the spleen， emolliating the liver， relieving pain， and checking diarrhea， and is mainly used in the treatment of gastrointestinal diseases such as irritable bowel syndrome （IBS） and ulcerative colitis （UC）. In addition， it is effective in treating gastrointestinal disorders with mental and psychological abnormalities， as well as obstinate anorexia in children， depression syndrome， and respiratory diseases. Experimental research and clinical practice have shown that Tongxie Yaofang has multi-component， multi-pathway， and multi-target characteristics in the treatment of diseases. The mechanism of Tongxie Yaofang in treating diseases is mainly attributed to anti-inflammation， immune function regulation， intestinal hypersensitivity improvement， emotion regulation， etc. Monoterpene glycosides， flavonoids， chromones， lactones， and other components contained play an important therapeutic role. The research on the systems biology of Tongxie Yaofang， such as metabolomics， proteomics， and network pharmacology， provides a scientific basis for clarifying its mechanism of action and expanding its clinical application. However， there are still some problems to be solved， such as difficulty in combining diseases and syndromes and lack of in-depth systematic research. Through the retrieval and collation of relevant literature， this paper systematically reviewed the material basis， pharmacological effects， and systems biology research of Tongxie Yaofang， aiming to lay a foundation for in-depth research on its mechanism in treating diseases and rational application in clinical practice.