Dear Ben

10 cysteinesss!! Umhhh hard work!!

Are you sure that all 10  are surface exposed?  Is it strange that you have so many exposed cysteines not involved in S-S. Which is they role? metal binding? 

There is not a simple approach to solve your issue and % is success is low. 

In my mind i have 2 ways:

1) Mutate all the other cisteines (mutation Cys to ser) and wish that the mutations  not change a lot the structural integrity of your protein. Is this an enzime? have you an assay to compare WT vs mutant? 

Do you have the protein structure? The other cysteines where are located? in loops? 

2) Using the WT protein:

In case the cisteine 2 and 5 form an intramolecular S-S you can try to limit the aspecific inter molecular S-S formation just  performing oxidation at very low protein concentration and therefore minimize the probability of intermolecular S-S bonds.  if you succed try to block the exposed cysteines with a reagent as iodoacetamide (IA) or derivates. 

But if i well understood this is not your case. Also the cysteine 2 and 5 form inter-molecular disulfide and lead to dimerization? 

In this case you have to hope that the stability and therefore the reduction potential of the specific S-S is  higher respect than the aspecific S-S bonds and by use different GSH/GSSG ratio you are able to find out one conditions that allow you the formation of the correct S-S.

If you are able to obtain this form, you can try to protect the other cisteine with a reagent as iodoacetamide and in this way stabilize your conformation.

But it is something hard and you need a lot of luck, also because theoretically to work with GSH/GSSG you need to operate in a anaerobic chamber with oxygen free solutions. 

good luck!

Manuele