Final answer:
LMP2 and LMP7 are proteins incorporated into the proteasome of stressed cells, such as those infected by viruses or transformed into tumor cells, to aid in immune response.
Step-by-step explanation:
The question is referring to the composition of proteasomes in cells, with specific reference to the proteins LMP2 and LMP7. These are not components of the proteasome in healthy cells; rather, they are typically incorporated into the proteasome in cells that are under stress, such as those infected by viruses or transformed into tumor cells. In the context of an infection or transformation, there can be alterations in MHC I molecules, making it difficult for the cell to present these molecules on the cell surface as it normally would. Viruses can produce proteins that interfere with MHC I processing and trafficking, reducing their presence on the cell surface. This signals to natural killer (NK) cells that the cell is 'unhealthy' or 'abnormal' and results in immune surveillance.
In such stressed cells, the replacements of certain proteasome subunits with LMP2 and LMP7 enable the production of different types of peptides that can be presented by MHC I molecules to T cells. This is an immune response to help the body identify and eliminate cells that have been infected or have undergone malignant transformation.