Schematic representation of signal transduction modification by MHC class I open conformers in medulloblastoma. The closed conformation of MHC class I (left) is composed of the heavy chain possessing three extracellular domains (α1, α2 and α3) non-covalently bound to β2m (β2) and antigen peptide (pep). Dissociation of β2m and peptide leads to the formation of open conformation that can interact with receptors (R) on the cell surface. This interaction dulls the impact of receptor ligand (L) binding (here symbolically represented by binding of one unit of ligand per one unit of receptor; note, however, that the impact of open conformers may not be related to ligand binding, but some other mechanism, i.e. preventing optimal receptor conformation). Binding of extracellular β2m to open conformer releases the receptor, enabling full blown signaling indicated by increased phosphorylation (P) of intracellular portion of the receptor.