Cell Biology: Protein Translocation and Glycosylation

Intracellular Trafficking

• Intracellular trafficking refers to the movement of molecules within the cell
• Key components involved: COPI and COPII coat proteins, regulating anterograde and retrograde transport in the early secretory pathway

Protein Translocation and Glycosylation

• Signal sequence or signal peptide: a stretch of 12-16 hydrophobic amino acids at the N-terminus flanked by basic "charged" residues
• Signals and enzymes involved: signal peptidase removes the signal peptide after translocation into the ER
• Cellular location: Endoplasmic Reticulum (ER)
• Motifs: hydrophobic regions, signal sequence, and transmembrane domains

Importance of Intracellular Trafficking

• Pathogens exploit cellular machinery for protein production and transport
• Cell biology plays a crucial role in the location and detection of pathogens and the activation of immune response
• Secretory pathway is crucial during pathogen infection for protein production and localization

Virology and Immune Responses

• Release of virus particles involves the secretory pathway
• ER and Golgi apparatus are involved in protein modification during virus replication
• Immunoglobulin production and secretion occur through the secretory pathway

mRNA Vaccines

• Signals within the protein direct it to the secretory pathway and ultimately presented at the cell surface for immune surveillance
• Nanoparticle is taken into cells, and the mRNA is released and translated on host ribosomes

Transmembrane Proteins

• Proteins with additional hydrophobic regions can embed within the membrane
• Multiple "membrane spanning" or "transmembrane" domains may exist within a protein
• The greater the hydrophobicity of the protein, the greater the affinity for the membrane

Intracellular Transport

• Highly regulated and dynamic processes exist to move constituents in and out of the cell
• Reasons for transporting molecules in cells:
  • Residency: proteins made in the ER may have a function elsewhere
  • Secretion: molecules are expelled into the extracellular environment
  • Required upon stimulation: e.g., hormone release

Secretory Pathway

• Used to move materials around the cell, including the plasma membrane and outside the cell
• Proteins destined for the PM, endosomes/lysosomes, or secretion are synthesized by the RER
• Contain specific amino acid sequences (signal sequences) which target them to the lumen of RER

This quiz covers the key components of intracellular trafficking, regulation of anterograde and retrograde movement, and the process of protein translocation and glycosylation, including signals, enzymes, and cellular locations involved.