CD3E&CD3D Heterodimer, Fc, His Tag&Fc, Flag Tag Protein, Mouse

CD3ε and CD3γ are two essential and homologous subunits of the T cell receptor (TCR) complex. They are type I transmembrane glycoproteins belonging to the immunoglobulin superfamily. Unlike the variable TCRαβ or TCRγδ chains that recognize antigens, CD3ε and CD3γ, along with CD3δ and the ζ-chain homodimer, form the invariant CD3 signaling module.

These subunits exist primarily as a CD3εγ heterodimer on the cell surface. Their primary function is to mediate signal transduction from the engaged TCR to the T cell interior. Each subunit contains three immunoreceptor tyrosine-based activation motifs (ITAMs) in their cytoplasmic tails. Upon TCR-pMHC engagement, these ITAMs are phosphorylated by Src-family kinases, initiating a downstream cascade that leads to T cell activation, proliferation, and differentiation.

Structurally, the CD3εγ heterodimer plays a critical role in the assembly, surface expression, and conformational stability of the TCR complex. Their extracellular immunoglobulin domains interact with the TCRαβ constant regions, while their unique transmembrane charged residues are crucial for interactions within the complete TCR-CD3 assembly. CD3γ is particularly notable for having a conserved di-leucine-based motif in its cytoplasmic tail that can mediate TCR-CD3 complex internalization and downregulation, a key mechanism for modulating T cell responses. Defects in CD3γ are a known cause of severe combined immunodeficiency (SCID). The CD3εγ pair is also a stable surface marker for T cells.