Hi Tong Zhou,

I would say it is case dependent. In vivo some of the proteins form transient dimers or ligand dependent dimers. In some cases dimerization could be very dynamic i.e. the proteins are in constant association-dissociation phase and so it is absolutely case dependent. Also, you will find differences in association behavior for soluble and membrane associated proteins. I hope I answered your question.

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Best,

Kalpana 

On the one hand it may  be really difficult to know. On the other hand , if possible it will depend on the specific protein. And finally, hemoglobin (not dimer but tetramer) has been quite extensively studied and I would think that it is not expected that hemoglobin dissociates into monomers.

Hi there,

The only way I could think of is to make the cell permeant to a molecule able to specifically disrupt the targeted protein interaction or even to trigger the cell to synthetize this molecule ...

It's very challenge to study this and only if dimerization or dissociation would related to its in vivo function in e.g. your animal /disease model.  I could think about a few approaches but the interpretation could be difficult or even misleading even if you could have all the tools or reagents needed:

-Immunohistochemistry tissue stain with antibody or EM

-cultured cell antibody staining with imaging analysis (DR. Liger's answer)

-mutating potential amino acid residues involving in dimerization

-isolate proteins from tissue in its native form

-predict in vivo behavior based on in vitro study of protein properties 

Agree with Dr. Pandey, it's high dependent on individual proteins and dimerization could highly influenced by protein localization and may or may not be related to its physiological roles.

A good system to look at are those heterodimers which may have very distingue function comparing monomers.  Mutation of a gene products may also contribute to the dimerization or dissociation.

There are numerous well studied membrane proteins/receptors, where dimerization are essential for response to the ligand and down-stream effects.

In vitro data (isolated protein) should give you good indication of possible behavior in vivo but could not be certain due to much higher/lower protein concentration and post-translational modification of the protein monomers and unknown in vivo binding partners and cellular/tissue matrix structure and interaction with target protein. 

Are you asking about natural processes and disease states or injecting a protein that dimerizes?  There are examples of oligomerization of proteins which naturally associate and dissociate such as receptors or go through this process in a disease state such as Alzhiemer's.  If a protein is injected and dimerizes to itself or other proteins, covalently or non-covalently, there will likely be an equilibrium between monomer and dimeric states but that equilibrium may be shifted well to dimer formation if this is what you are referring to.

It is very case dependent. Of course, for many systems cells have evolve mechanisms for regulating protein-protein interactions, e.g. by production of alternative interaction partners, by allosteric regulation, by phosphorylation.