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H. sapiens mIgM B Cell Receptor

spinqualitylabelsall models B-Cell Receptor (7XQ8) Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structure Heavy Chain Interactions (Iga and IgB) While the antigen binding site structure of the mIgM BCR is identical to other common soluble antibodies, there are several intracellular interactions between the heavy chains and Iga/B subunits that make it unique. In the Fc portion of the structure, the two heavy chains interact via a disulfide bond and form an O-shaped ring. Additionally, the Fc portion binds the Ig''a/B'' heterodimer with 1:1 stoichiometry (reference link Pavel and Susan). Due to the orientation of the heavy chains in the O-shaped ring, only Heavy chain 1 (Hc1) forms direct interactions with the Iga/B heterodimer. Furthermore, Hc1 and Iga interact through two hydrogen bonds which are stabilized by sandwiching of aromatic residues. Similarly, Hc1 and IgB interact through three hydrogen bonds. The residues involved in the interactions at the heavy chain and Iga/B interface are highly conserved across all species, suggesting a conserved mode of interaction (reference link Qiang "IgM B cell receptor"). The Iga/B heterodimer is an obligate component of all BCRs. Iga and IgB non-covalently associate with mIgM, and are crucial components for initiating biochemical signaling inside the B cell upon antigen binding (reference link Pavel and Susan). Iga and IgB are associated by a disulfide bond between cystine residues. The disulfide bond is stabilized by π-π stacking and a hydrogen bond. These residues are highly conserved across species, suggesting conservation of the Iga/B interface.