Robert J. Bradbury, <firstname.lastname@example.org>, writes:
> On Mon, 6 Sep 1999, Technotranscendence wrote:
> > On Sunday, September 05, 1999 11:20 PM "Hal" email@example.com wrote:
> > > It is interesting to learn that the reason proteins are able to get
> > > into cells is because they are capable of unfolding.
> Hal, I think you are making a stretch here unless you have some
> source I'm unaware of. I've briefly glanced at Dowdy's papers
> on the TAT fusion proteins and he claims the mechanism isn't
> currently known. He does cite one paper that "claims" the
> uptake is not receptor mediated. But Not-receptor-mediated
> does not equal protein-unfolding.
It is probably an oversimplification to suggest that protein unfolding is the only mechanism. However it does appear to play an important role in many cases.
> This does clearly occur in some circumstances, particularly protein
> import into the mitochondria. However, there are protein channels
> and chaperones that actively manage this process. Whether there
> are similar active single-threaded channels, as opposed to large
> molecule absorbing "caves", in the outer membrane isn't clear at this time.
One note, from
http://www.portlandpress.co.uk/books/isbn/1855781212.htm, is that 95% of the cell's lipid membranes are found internally, separating cellular compartments (mitochondria and other organelles, endoplasmic reticulum, the nucleus, etc.). So whatever method is used to pass through lipid membranes would be needed even more within the cell than for getting inside.