Disulfide engineering at the dimer interface of Lactobacillus casei thymidylate synthase: Crystal structure of the T155C/E188C/C244T mutant

The crystal structure of a covalently cross-linked Lactobacillus casei thym idylate synthase has been determined at 2.8 Angstrom resolution. The sites for mutation to achieve the bis-disulfide linked dimer were identified usin g the disulfide modeling program MODIP. The mutant so obtained was found to be remarkably thermostable. This increase in stability has been reasoned t o be entirely a consequence of the covalent gluing between the two subunits .