Abhinaya,

Regardless of the N-terminal targer sequence, there is lot of speculation on other constitutents of a protein influencing its localization. For the transmembrane proteins, for instance, it additionally would be the size (lenght; span) of the transmembrane domains (look up Federica Brandizi's papers). For the chloroplast proteins (so, evolutionary somewhat similar to mitochondria), already few years back I prepared a seminar on the topic: not only were the N-term and transmembrane domains involved, there was also C-term sequence affecting the chl. localization.

In case of soluble proteins, I guess pH would be of influence (charges =>protein folding!), but I am not an expert on these.

The protein has to pass thorugh the golgi apparatus from ER before it is secreted out. The secreted protein is then transported through cytoskeletal proteins,namely actin fillaments, tubulin microtubules (and intermediatory filaments in cells of mesenchymal orgin) although cytoskeletal independent vesicular/energy dependant transport do exists. In case of protein destinied for mitochondria contains a specific signal sequence which is recognized by a mitochondrial stimulation factor chaperone and transports to its recepetor on the outer membrane of mitochondria.

A mitochondrial protein may have an N-terminal signal peptide, but this is NOT the same as the hydrofobic N-terminus that leads to protein transfer to the ER based on recognition by the SRP and insertion into the secretion channel. The signal peptide for mitochondrial matrix translocation is an amphipatic alpha-helix, and the positive redisues in the hydrofilic face of this helix assist in the proper insertion in the mitochondrial inner membrane, making use of the PMF there, and the translocation complexes TOM and TIM. I suggest you read up on both these processes in a standard molecular cell biology book (Alberts 5th edition chapter 12). The proteins are recognized in the cytosol, and do NOT pass through the secretory pathway.

Hello All, thank you for your inputs. I understand the various modules and channels via which protein translocation happens, what I'm interested in discussing here is how they happen, difference between the anterograde and retrograde transports. I do not specifically want to restrict the discussion to mt targetted transport. I'm also interested in transport within the nucleus.

@Mr Moothy, thank you for getting my context right, cytoskeletal prtrn mediated transport is what I'm looking out for. I request you to check this amazing paper ('Kinesin superfamily motor proteins and intracellular transport' - Nobutaka Hirokawa et al, 2009) http://www.ncbi.nlm.nih.gov/pubmed/19773780 which describes,

1. axioplasmic transport, 2. non-polarized cell transport, 3. Anterograde and retrograde. 4.Various adaptors and ptrns and other cystokeletal motors carrying out transport, 5. organelle transport, 6. Vesicular transport, 7. Plus and minus end mediated microtuble transport 8. protein recognition to the microtibule assembly etc.

What I'm trying to further my understanding upon is primarily on,

1. How the adaptor and scaffold proteins facilitate the correct bonding between the released protein molecules as they are released from the ER/golgi vesicles.

2. How does the molecular motor facilitate movement?

3. How does the plus and minus end microtibule facilitate movement - via charge if so how? Are there any mechanisms which is detailed out?

Do let me know your understanding on these various processes.