Signaalisarjoista

Signaalisarjoista, often translated as signal sequences or signal peptides, are short stretches of amino acids typically found at the N-terminus of newly synthesized proteins. Their primary function is to direct these proteins to specific cellular locations, such as the endoplasmic reticulum, mitochondria, or chloroplasts. This targeting is crucial for proper protein folding, function, and secretion.

The process begins when a signal sequence emerges from the ribosome during protein synthesis. This sequence is then recognized by a signal recognition particle (SRP), which binds to both the ribosome and the signal sequence, temporarily halting translation. The SRP-ribosome-mRNA-nascent polypeptide complex then docks with a specific receptor on the target organelle membrane.

Upon docking, the SRP is released, and translation resumes, with the growing polypeptide chain threaded through a protein translocator channel in the membrane. Once the protein has entered its destination or been fully synthesized, the signal sequence is usually cleaved off by a signal peptidase enzyme, rendering the mature protein functional and released from the targeting machinery. Different signal sequences have specific recognition motifs that ensure proteins are directed to their correct compartments within the cell. Defects in signal sequences can lead to mislocalization of proteins, resulting in various cellular dysfunctions and diseases.