proteinexport

Protein export is the cellular process by which newly synthesized proteins are transported from their site of synthesis to their functional destinations. In eukaryotic cells, the dominant route directs many proteins through the secretory pathway, which includes the endoplasmic reticulum (ER) and the Golgi apparatus before reaching the cell surface or being released from the cell. Export decisions are guided by signal sequences and protein architecture that determine whether a protein will be secreted, membrane-anchored, or delivered to organelles.

The classical secretory pathway: Proteins destined for secretion or membrane insertion typically begin with an N-terminal signal peptide. The signal is recognized by the signal recognition particle (SRP), which pauses translation and targets the ribosome to the ER. Through the Sec61 translocon, the protein is threaded into or across the ER membrane, where it folds and undergoes quality control and often N-linked glycosylation. COPII-coated vesicles carry the protein to the Golgi apparatus, where it is modified and sorted. At the trans-Golgi network, cargos are packaged into vesicles that fuse with the plasma membrane to deliver soluble proteins by exocytosis or to insert membrane proteins.

Non-classical secretion and alternative routes also exist. Some proteins lack an ER signal peptide and are secreted via unconventional pathways that bypass the classical ER–Golgi system. Others are secreted within extracellular vesicles, such as exosomes, or reach the cell surface through lysosome-related pathways. In addition, proteins can be targeted to specific organelles via distinct signals and receptors, where they perform intralumenal or membrane-associated functions.

Biological significance and applications: Protein export is essential for intercellular communication, immune responses, and tissue remodeling, as well as for the biotechnological production of secreted recombinant proteins. Disruptions in trafficking can contribute to disease, including cystic fibrosis and various congenital disorders of glycosylation. Researchers study export pathways to understand cell biology and to optimize therapeutic protein manufacture.