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