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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 The BCR consists of a membrane-bound immunoglobulin (mIg) and two signal-transducing subunits, Igα and Igβ. The mIg consists of two heavy chains and two light chains. Antigen binding at the binding site triggers signal transduction by Igα and Igβ. Both consist of an extracellular, Ig-like domain, and an intracellular immunoreceptor tyrosine-based activation motif. . Heavy Chain Interactions (Igα and Igβ) While the antigen binding site structure of the mIgM BCR is identical to common soluble antibodies, intermolecular interactions between the heavy chains and Igα/β subunits provide the emergent receptor properties. 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 α/β heterodimer (heterodimer zoomed) with 1:1 stoichiometry. . Due to the orientation of the heavy chains in the O-shaped ring, only Heavy chain 1 (Hc1) forms direct interactions with the Igα/β heterodimer. To correspond with the 3D representations, Hc1 residues will be represented in blue, Igα residues will be represented in red, and Igβ residues will be represented in orange. Furthermore, Hc1 and Igα interact through two hydrogen bonds (T75-Q487 and N73-Q493) which are stabilized by sandwiching of aromatic residues (W76 sandwiched between F358 and F485). Similarly, Hc1 and Igβ interact through three hydrogen bonds (Y66-R491, K62-T530, and R55-T533). The residues involved in the interactions at the heavy chain and Igα/β interface are highly conserved across all species, suggesting a conserved mode of interaction. . The Igα/β heterodimer is composed of a transmembrane domain, which consists of two hydrophobic helices, and an extracellular domain, which forms an interface with and Hc1. The Igα/β heterodimer is an obligate component of all BCRs. Igα and Igβ non-covalently associate with mIgM, and are crucial components for initiating biochemical signaling inside the B cell upon antigen binding. . Igα and Igβ are connected by a disulfide bond between cystine residues (C119-C136). The disulfide bond is further stabilized by π-π stacking (Y122 and F52) and a hydrogen bond (G120-R51). These residues in Igα/β are highly conserved across species, suggesting conservation of the Igα/β interface. . TextToBeDisplayed Function Proposed Conformational Changes .