I am getting slightly confused with all of the terms above and was wondering if someone could see if I have got this right:
- I think transport from the ER to Golgi is almost always from the plus end of a microtutbule to the minus end, and therefore is carrier by a dynein. I think this is signalled by a COP1 protein, which can attach to the dynein for transport. I think that this is retrograde trnsport as it is from the plus end to the minus end, however this I am really not sure about.
- Conversely, I think that transport from the Golgi to the ER, being from the minus end to the plus end, is carrier by kinesis and therefore the COP2 protein which attaches to the kinesis carries these vesicles. I think this is an example of anterograde transport.
My confusion lies in the fact that
I am not sure whether retrograde and anterograde transport refer to movement from plus and to minus end of a microtubule or vice versa (respectively) or whether they refer to general motion of cargo into and out of the cell (respectively). For example, if a vesicle was being transported from the plasma membrane to the Golgi and then to the ER, the first part of this journey would be along the plus end to the minus end of the microtubule, carrier by dyneins; the second part of the journey from Golgi to ER would be from minus and to plus and and therefore carried by kinesis. Would this transport therefore initially be retrograde and then anterograde, or do these terms simply refer to the general direction of motion of cargo into/out of a cell and therefore this whole motion would be described as retrograde?
- Secondly, if I remember correctly my lecturer said that one of the COP proteins takes proteins from the Golgi to the ER and the other takes froteins from the ER to the Golgi to the plasma membrane. This is confusing me because it would mean that the same COP protein would take a vesicle from plus end to minus end of a microtubule from ER to Golgi, and then from minus end to plus end from Golgi to the plasma membrane, which surely can't be right as the same protein should not be recognised by the two different motor proteins, right? However if it were the other case, that say COP 1 takes vesicles from ER to Golgi and COP 2 takes them from Golgi to ER OR from the Golgi to the plasma membrane, what would distinguish whether the cargo was taken to the plasma membrane or back to the endoplasmic reticulum?
Thank you in advance!