Synthesis
During synthesis of class II MHC in the endoplasmic reticulum, the α and β chains are produced and complexed with a special polypeptide known as the invariant chain. The nascent MHC class II protein in the rough ER has its peptide-binding cleft blocked by the invariant chain (Ii; a trimer) to prevent it from binding cellular peptides or peptides from the endogenous pathway (such as those that would be loaded onto class I MHC).
The invariant chain also facilitates the export of class II MHC from the ER to the golgi, followed by fusion with a late endosome containing endocytosed, degraded proteins. The invariant chain is then broken down in stages by proteases called cathepsins, leaving only a small fragment known as CLIP which maintains blockage of the peptide binding cleft on the MHC molecule. An MHC class II-like structure, HLA-DM, facilitates CLIP removal and allows the binding of peptides with higher affinities. The stable class II MHC is then presented on the cell surface.
Read more about this topic: MHC Class II
Famous quotes containing the word synthesis:
“Our art is the finest, the noblest, the most suggestive, for it is the synthesis of all the arts. Sculpture, painting, literature, elocution, architecture, and music are its natural tools. But while it needs all of those artistic manifestations in order to be its whole self, it asks of its priest or priestess one indispensable virtue: “faith.””
—Sarah Bernhardt (1845–1923)
“In order to begin an analysis, there must already be a synthesis present in the mind.”
—Johan Huizinga (1872–1945)
“The spider-mind acquires a faculty of memory, and, with it, a singular skill of analysis and synthesis, taking apart and putting together in different relations the meshes of its trap. Man had in the beginning no power of analysis or synthesis approaching that of the spider, or even of the honey-bee; but he had acute sensibility to the higher forces.”
—Henry Brooks Adams (1838–1918)