It is comparatively easy to tell a cell's state of health: On their surface, cells present fragments of almost all the proteins they contain inside. This means the immune system can directly recognize whether a cell has been infected by a virus or has been dangerously altered by a mutation . Countless molecular "radio masts" - the MHC-I molecules - are responsible for presenting these fragments.
They are assembled inside the cell and then transported to the membrane, the lipid layer surrounding the cell. Here, the masts are anchored such that the cargo faces outside and can be detected by troops of the immune system constantly patrolling the body. If these troops detect harmful molecules being presented on the MHC-I radio masts, they kill the relevant cell.
A requirement, however, is that the masts themselves are fully functional; otherwise, there is a risk that this mechanism will not work and harmful cells escape the immune system. "We have now discovered a sensor inside the cell that ensures that only functional MHC-I molecules are transported to the plasma membrane, while the defective units are eliminated," explains Dr. Lina Herhaus, who until recently conducted research on this topic at Goethe University's Institute of Biochemistry II and is now leading an independent research group at Braunschweig-based Helmholtz Centre for Infection Research.
Cells continuously produce a large number of proteins to sustain their manifold functions. If errors occur during this process,.