Protein/protein-crosslinkers

[Peter Henriksen]

I am trying to design an experiment in which I will need to make protein-protein crosslinks but not DNA-protein crosslinks in living cells. 
 
In principal I think this should be possible using a crosslinker that will crosslink between two carboxylic groups but I haven't been able to find such a crosslinker so far.
 
If anyone has knowledge of a crosslinker with the above properties I would be thrilled to know about it. 
 
Thanks
 
Peter Henriksen