Final answer:
MCH class I has one protein, which is a glycoprotein made up of a heavy chain and beta-2 macroglobulin, crucial for antigen presentation to T lymphocytes and immune system signaling.
Step-by-step explanation:
The MCH class I has one protein, which is a complex glycoprotein integral to the immune response. This protein is composed of a heavy chain paired with the smaller beta-2 microglobulin (β2m) component. The heavy chain of the MCH I molecule includes three domains: α1, α2, and α3, but only the heavy chain spans the cytoplasmic membrane. The antigen-binding cleft of MHC class I molecules, which is crucial for presenting antigens to T lymphocytes, is formed by the α1 and α2 domains. These molecules are found on the surface of all nucleated cells and play a vital role in signaling to the immune system whether a cell is healthy or compromised, such as by infection or cancer. The complex and diverse genotypic landscape of the MHC I molecules is highlighted by the discovery of over 1500 alleles, leading to more than 2000 possible MHC I protein components, each potentially responsible for a vast array of antigens that the immune system must recognize.