An overall negative charge on the proteins. Since SDS is negatively charged, it masks the intrinsic charge of the protein it binds
A similar charge-to-mass ratio for all proteins in a mixture, since SDS binds at a consistent rate of 1.4 g SDS per 1g protein SDS (a stoichiometry of about one SDS molecule per two amino acids)
A long, rod-like conformation on the proteins instead of a complex tertiary shape