Editing Protein targeting (section)

== History ==
[[File:Gunter Blobel 2008 3.JPG|thumb|282x282px|Günter Blobel, awarded the 1999 Nobel Prize in Physiology for his discovery that proteins contain intrinsic signal sequences.]]
In 1970, [[Günter Blobel]] conducted experiments on protein translocation across [[membrane]]s. Blobel, then an assistant professor at [[Rockefeller University]], built upon the work of his colleague [[George Emil Palade|George Palade]].<ref name="Leslie-2005">{{cite journal | vauthors = Leslie M | title = Lost in translation: the signal hypothesis | journal = The Journal of Cell Biology | volume = 170 | issue = 3 | pages = 338 | date = August 2005 | pmid = 16167405 | pmc = 2254867 | doi = 10.1083/jcb1703fta1 }}</ref> Palade had previously demonstrated that non-secreted proteins were translated by free [[ribosome]]s in the cytosol, while secreted proteins (and target proteins, in general) were translated by ribosomes bound to the [[endoplasmic reticulum]] (ER).<ref name="Leslie-2005" /> Candidate explanations at the time postulated a processing difference between free and ER-bound ribosomes, but Blobel hypothesized that protein targeting relied on characteristics inherent to the proteins, rather than a difference in ribosomes. Supporting his hypothesis, Blobel discovered that many proteins have a short [[Protein primary structure|amino acid sequence]] at one end that functions like a postal code specifying an intracellular or extracellular destination.<ref name="Blobel-1975" /> He described these short sequences (generally 13 to 36 amino acids residues)<ref name="Nelson-2017" /> as [[signal peptide]]s or signal sequences and was awarded the 1999 [[Nobel Prize in Physiology or Medicine|Nobel prize in Physiology]] for the same.<ref>{{Cite web|title=The Nobel Prize in Physiology or Medicine 1999|url=https://www.nobelprize.org/prizes/medicine/1999/summary/|access-date=2020-09-19|website=NobelPrize.org|language=en-US}}</ref>