סקירה כללית של מיון והובלת חלבונים

Protein sorting occurs during translation or after protein synthesis by two distinct processes: signal-based sorting and vesicle-based trafficking. Signal-based sorting employs two modes of transport: gated transport and protein translocation.

Nuclear proteins are actively transported from the cytosol to the nucleus via the nuclear pore complexes embedded in the nuclear envelope. This process is called gated transport.

These proteins contain specific amino acid sequences called sorting signals that are recognized by a sorting receptor that transports the protein to the nucleus.

Proteins targeted to the chloroplasts, mitochondria, and endoplasmic reticulum are imported through translocons, specialized transmembrane proteins, in a process called protein translocation.

During translocation, chaperone proteins in the cytosol bind to the target protein and deliver it to the membrane, where the sorting signals are recognized by the import receptors of the translocon. Using ATP hydrolysis, the target protein is unfolded and transported through a channel in the translocon to reach its destination within the organelle.

In vesicular trafficking, soluble proteins are packed from the endoplasmic reticulum lumen and loaded onto membrane-bound transport vesicles.

Transport vesicles bud off from the endoplasmic reticulum membrane and fuse with the Golgi membrane or the cell membrane without crossing the lipid bilayers to deliver the proteins to their target location.