What is the main role of signal sequences in protein trafficking?

Signal sequences play a critical role in ensuring that proteins are delivered to their appropriate cellular destinations. These short, often hydrophobic peptide sequences are located at the N-terminus or sometimes within the protein. Signal sequences act as molecular addresses, instructing the cell's machinery where the proteins need to go within the cell. For example, a signal sequence might guide a newly synthesized protein to the endoplasmic reticulum for proper folding and subsequent transport to the Golgi apparatus, or even direct it to lysosomes or the plasma membrane.

Once the protein's signal sequence is recognized by specific receptor proteins, it can be efficiently transported across membranes. This specificity is essential because misfolded or misrouted proteins can lead to cellular dysfunction or disease. In summary, signal sequences are essential for the correct trafficking of proteins, ensuring that they reach their intended sites of action within the cell, contributing to proper cellular function and organization.