 Hi, this is Jin Hualu from the National Institute of Energy and Infectious Diseases. In this video, I am going to highlight our latest application in protein science entitled Contraction and IGA Shear Abundant Hotspot on FC Alpha-1. FC receptors recognize the FC portion of antibodies in humans. The most abundant antibodies are IgG and IgA. The cognate receptors are FC Gamma receptors and FC Alpha-1, which are respectively shown by blue, red and green cartons here. All the FC receptors are distantly related by sharing overall band structures in the first two IgG-like domains. IgG-FC refers to the D2 domain of FC Gamma receptors. The stoicometry is one-to-one, necessitating reset cross-linking for activation. However, IgG bonds to the D1 domain of FC Alpha-1 and the stoicometry is two-to-one. Their interfaces in the crystal structures are highlighted by sign surface here. In our previous publication, we found that contractions can also interact with FC Gamma receptors. Contractions are characterized by a pentamericate ring-like structure bearing five identical subunits. In addition, contractions C-reactive protein and serum amnolip are two major acute-fuse proteins in humans and mice respectively. In a crystal structure, SAP bonds to both D1 and D2 domains of FC Gamma receptors. Of the bonding screening of other FC receptors, we identified FC Alpha-1 as another functional receptor for contractions. Based on the crystal structure of SAP FC Gamma 2A complex, we created a docking model of CRB FC Alpha-1 complex. In this model, CRB bonds to both D1 and D2 domains of FC Alpha-1 in a similar mode as FC Gamma receptors. We identified six clusters with 11 potential contacting residues on FC Alpha-1. In this study, we carried out metagenesis studies to evaluate the contribution of each individual cluster to the bonding of contractions. Interestingly, practitioners including IGA bonding residues on the D1 domain significantly decreased the bonding of both contractions and IGA. Therefore, contractions and IGA share a bonding hotspot on FC Alpha-1. We summarize our current understanding of the function of FC receptors and their ligands. Contracting interactions with FC receptors provide additional pathways for the recognition of nuclear sites expressing these receptors. These innate immune interactions are expected to occur prior to the development of antibodies. A possible function is the promotion of phagocytosis as depicted in this animation. In the animation, C-reactive protein and IgG recognize and bond to a bacterium. The oxalins are recognized by FC receptors on the membrane of a phagocytic cell. The bonding of the oxalized bacterium to these receptors results in phagocytosis.