I want to digest a tagged protein with TEV protease, it has disulfide bridges. Is there any way of doing cleavage without DTT?
Yes, no problem. TEV is slowly inactivated oxidation of the active site cysteine but that's about it. If you absolutely must have no reducer during cleavage, simply up the amount of the enzyme. But it's almost certain that most proteins with S-S bridges will be perfectly happy at low reducer concentration (0.2 mM TCEP, 1 mM DTT or something along these lines; particularly if there is more than one bridge - mass action is a powerful thing and, e.g., IgG has no problem at 10 mM DTT). So I wouldn't worry about it - just add enough TEV under conditions that make your protein happy.
Dima
