What is the structure of a T cell receptor?

The T-cell receptor (TCR) is a heterodimer. It is composed of two polypeptide chains that together make up one antigen binding region. About 95% of TCRs are made up of an alpha (α) and a beta (β) chain (encoded by TRA and TRB genes respectively), while the remaining 5% are made up of gamma (γ) and delta (δ) chains (encoded by TRG and TRD genes respectively). 

Each TCR chain has two domains, with an intra-chain disulfide bond spanning 60 to 75 amino acids. The structure of TCR is stabilized by the disulfide bond that links the two chains together. 

Both TCR chains also possess a short cytoplasmic tail of 5-12 amino acids at the carboxyl terminal end. 

These structural elements are critical for the TCR's function in recognizing and binding to specific antigens presented by antigen-presenting cells, which initiates the T-cell's immune response. Key features called complementary determining regions (CDRs) within the variable region contribute to the specificity of antigen binding.