MHC-I Processing | Antigen Processing and Presentation

Summary

This video explains the intricate process of MHC antigen processing and presentation, key to the immune response. The video covers how MHC molecules are assembled in the endoplasmic reticulum, the degradation and processing of foreign pathogens into peptides, and their eventual presentation on the cell surface. It also delves into the roles of chaperone proteins like calnexin and calreticulin, peptide transport, and loading by the TAP complex. The immune system then recognizes these peptides via the T-cell receptor, initiating a response that may lead to cell apoptosis to eliminate the threat.

Takeaways

• 😀 MHC molecule maturation involves the assembly of light and heavy chains in the endoplasmic reticulum.
• 😀 Pathogenic proteins are processed via ubiquitination and proteosomal degradation to form small peptides.
• 😀 The small peptides (around 15 amino acids) are presented on the cell surface by MHC class I molecules.
• 😀 Calnexin stabilizes nascent MHC heavy chains and assists in glycoprotein folding in the endoplasmic reticulum.
• 😀 The MHC molecule structure consists of three domains in the alpha chain: alpha 1, alpha 2, and alpha 3.
• 😀 Beta 2 microglobulin binds with the MHC heavy chain to complete the MHC class I molecule structure.
• 😀 Calreticulin replaces calnexin in the process, with ERP57 aiding the formation of disulfide bonds.
• 😀 After the MHC molecule's structure is stabilized, it associates with TAP (Transporter Associated with Antigen Processing).
• 😀 Small peptides (8-10 amino acids) are further edited and loaded into the MHC molecule for antigen presentation.
• 😀 The MHC-peptide complex is transported via the secretory pathway to the cell membrane, where it is presented to T cells.
• 😀 The TCR on another cell recognizes the MHC-peptide complex, leading to immune response activation and potential apoptosis of the pathogen-infected cell.

Q & A

What is the main topic discussed in the video?

The main topic discussed in the video is MHC (Major Histocompatibility Complex) event processing and antigen processing and presentation.

What role does the calnexin protein play in MHC processing?

The calnexin protein binds with the nascent MHC heavy chain, stabilizing its structure and aiding in the formation of disulfide bonds and the folding of the MHC molecule.

How does the MHC molecule complete its structure?

The MHC heavy chain binds with the beta-2 microglobulin (light chain), and this interaction, along with the help of chaperone proteins like calnexin and calreticulin, completes the structure of the MHC I molecule.

What happens to the pathogenic proteins once they enter the cell?

Pathogenic proteins are processed via ubiquitination and proteasomal degradation, breaking down into small peptides about 15 amino acids long.

What role do TAP and ERP 57 play in antigen processing?

TAP (Transporter Associated with Antigen Processing) transports the small peptides into the lumen of the endoplasmic reticulum. ERP 57, an enzyme, helps in forming disulfide bonds within the MHC molecule, stabilizing its structure.

How are the peptides processed inside the endoplasmic reticulum?

The peptides are further trimmed from 15 amino acids to 8-10 amino acids long by the ERP 1 and TAPBP proteins in a process known as peptide editing.

What is the purpose of loading peptides onto the MHC molecule?

The purpose of loading peptides onto the MHC molecule is to present foreign peptides on the cell surface for recognition by T cells, which is essential for immune response.

How does the MHC molecule reach the cell surface after peptide loading?

Once the MHC molecule is loaded with peptides, it is transported through the Golgi apparatus and reaches the cell surface via vesicular fusion.

What is the role of CD8 in antigen presentation?

The CD8 molecule aids in tethering the MHC molecule with the T cell receptor (TCR), facilitating the recognition of the antigen-MHC complex by the TCR of another cell.

What happens after the TCR recognizes the MHC-peptide complex?

Once the TCR recognizes the MHC-peptide complex, a signal is sent to trigger apoptosis, leading to the elimination of the infected or abnormal cell.