SDS is a very strong detergent, it is likely to denature all proteins it meets. Use different lysis protocol to keep your protein working (lysozyme, ultrasonic disruption, etc).
Yes, it should be. If your protein of interest is in inclusion bodies, you can dissolve it usind SDS, urea, guanidinium hydrochloride, etc. After solubilization, you should renature and refold it (typically by gradient decrease of denaturing agent) - this step needs to be optimized for given protein. I would try urea rather than SDS.