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Related Concept Videos

Diversity of Antigen Receptors01:28

Diversity of Antigen Receptors

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Antigen receptors are essential components of the immune system crucial in defending the body against foreign invaders. These receptors are present on the surface of B and T cells, enabling them to recognize antigens and mount an appropriate immune response.
Before encountering any antigen, lymphocytes express these receptors. On B cells, the antigen receptor is a membrane-bound antibody molecule called BCR; on T cells, it is a T cell receptor or TCR. B and T cell receptors are composed of two...
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Antibody Structure01:10

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Overview
Antibodies, also known as immunoglobulins (Ig), are essential players of the adaptive immune system. These antigen-binding proteins are produced by B cells and make up 20 percent of the total blood plasma by weight. In mammals, antibodies fall into five different classes, which each elicits a different biological response upon antigen binding.
The Y-Shaped Structure of Antibodies Consists of Four Polypeptide Chains
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B Cell Activation and Differentiation01:24

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The adaptive immune response, a sophisticated defense mechanism, relies on the activation and differentiation of B lymphocytes, or B cells. These processes enable our bodies to mount a tailored response against specific pathogens such as bacteria, free virus particles, toxins, and parasites.
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Antibodies, also known as immunoglobulins, are produced by B cells in response to foreign substances, such as bacteria and viruses. These proteins are critical for recognizing and neutralizing these substances, protecting the body from potential harm.
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Assembly of Signaling Complexes01:30

Assembly of Signaling Complexes

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Multiprotein signaling complexes are formed in a dynamic process involving protein-protein interactions at the cytoplasmic domain of transmembrane receptors or enzymatic and non-enzymatic proteins associated with the receptor. These complexes ensure the activation and propagation of intracellular signals that regulate cell functions.
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Protein Complex Assembly02:41

Protein Complex Assembly

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Proteins can form homomeric complexes with another unit of the same protein or heteromeric complexes with different types.  Most protein complexes self-assemble spontaneously via ordered pathways, while some proteins need assembly factors that guide their proper assembly. Despite the crowded intracellular environment, proteins usually interact with their correct partners and form functional complexes.
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Related Experiment Video

Updated: Aug 25, 2025

Studying Organelle Dynamics in B Cells During Immune Synapse Formation
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Structural principles of B cell antigen receptor assembly.

Ying Dong1,2, Xiong Pi1,2, Frauke Bartels-Burgahn3,4

  • 1Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA.

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|October 13, 2022
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Structural analysis reveals the B cell antigen receptor (BCR) architecture, detailing how immunoglobulin and signaling components assemble. This provides a foundation for understanding B cell signaling and developing targeted therapies for BCR-related diseases.

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A TIRF Microscopy Technique for Real-time, Simultaneous Imaging of the TCR and its Associated Signaling Proteins
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Area of Science:

  • Immunology
  • Structural Biology
  • Molecular Medicine

Background:

  • The B cell antigen receptor (BCR) is crucial for adaptive immunity, mediating antigen recognition and initiating intracellular signaling cascades.
  • The precise structural organization of the BCR, particularly the assembly of its immunoglobulin and signaling subunits, remains largely undefined.
  • Understanding BCR structure is vital for deciphering B cell activation pathways and developing therapies for autoimmune and oncological diseases.

Purpose of the Study:

  • To elucidate the molecular architecture of the B cell antigen receptor (BCR) using high-resolution cryo-electron microscopy.
  • To determine the structural basis for BCR assembly, focusing on the interactions between immunoglobulin and Igα/Igβ signaling components.
  • To provide a structural framework for understanding BCR signaling mechanisms and guiding the development of novel therapeutics.

Main Methods:

  • Cryo-electron microscopy (cryo-EM) was employed to determine the structures of full-length mouse IgM BCR and its Fab-deleted variant.
  • Detailed structural analysis focused on the ectodomain (ECD), transmembrane domain (TMD), and the interactions between immunoglobulin and Igα/Igβ subunits.
  • Interfacial analyses were conducted to infer the general organizational principles applicable across different BCR classes.

Main Results:

  • The cryo-EM structures reveal how the Igα/Igβ heterodimer associates with the immunoglobulin heavy chain ectodomain, primarily through Igα.
  • A tight four-helix bundle is formed at the transmembrane domain by the interaction of immunoglobulin heavy chains and Igα/Igβ subunits, exhibiting asymmetry.
  • The connecting peptide of the immunoglobulin heavy chain plays a critical role in guiding transmembrane domain assembly, and the Igβ ITAM's proximity to the TMD suggests potential autoinhibition.

Conclusions:

  • The study provides the first detailed structural insights into the B cell antigen receptor (BCR) organization, revealing a conserved assembly principle across BCR classes.
  • The elucidated structure explains the functional arrangement of BCR components, including the signaling Igα/Igβ heterodimer and its interaction with the immunoglobulin.
  • These findings establish a structural foundation for understanding B cell activation and offer a platform for designing targeted therapies for BCR-mediated diseases.