C H A P T E R 3 5 , F I G U R E 1 3
Major histocompatibility complex (MHC) proteins class
The MHC class
of antigen-presenting cells comprise two polypeptide chains,
and p. The a-polypeptide (-360 residues) (helices red,
(3 sheets dark yellow, and loops gray) has two extracellular domains shown here (cel and
and a transmembrane and
intracellular domain (a3, not shown). The a3 domain is structurally similar to the immunoglobulins. The non- MHC
gene-related protein, |32-microglobulin (99 residues), is shown in green on the right side of each structure. The other
subunits of the complex that are involved in T-cell receptor recognition are not shown. The figures are derived from the
coordinates published in the Protein Data Bank files 1AGD and 1AGB. (A) HIV-1 GAG peptide GGKKKYKL present-
ed on the surface of the MHC class II protein. The peptide is shown with the residues “space-filled”, the Lys residue, K
is colored cyan and marked by the arrow. (B) HIV-1 GAG peptide GGRKKYKL presented on the surface of the MHC
class II protein. The peptide is shown with the residues space-filled, the Arg residue, R is colored cyan and marked by
the arrow. Note that the position of the a helix (part of the cul domain) immediately adjacent to the Arg or Lys residues
has undergone a change in position (conformation change) and has a small helical segment (lower left) as a result of
this single-amino-acid substitution. Such sensitivity to small changes in antigen structure is critical to specificity.
C H A P T E R 3 5 , F I G U R E 1 4
Complex of MHC class
C H A P T E R 3 5 , F IG U R E 15
Major histocompatibility complex (MHC)
HTLV-1 peptide (antigen) and TcR. The MHC class I proteins bind and
proteins class II. The MHC class II proteins bind and present and present
present peptides that are synthesized inside the infected cell to T-cell
peptides that are synthesized outside the infected cell, i.e., peptides that are
receptors (TcRs) specific for the bound peptides. Interaction and stimula-
derived from proteins of the infecting organisms, bound to their specific T-
tion of T-cell proliferation occurs with CD8 positive, cytoxic Tc cells.
cell receptors (TcRs). Interaction and stimulation of T-cell proliferation
The figure is derived from the coordinates published in the Protein Data
occurs with CD4+ positive T cells (Figure 35-16). The figure is derived from
Bank file 1BD2.
the coordinates published in the Protein Data Bank file 1A6A.