A conserved hydrogen-bond network stabilizes the structure of Beta class glutathione trasferases.

We identified a network of hydrogen bonds that is conserved in the structures of bacterial Beta class glu- tathione S-transferases (GSTs). It is formed by three residues: a serine, a histidine and a glutamate, together with a water molecule that links the serine with the histidine. This network connects the first helix of the N-terminal glutaredoxin-like domain with the last helix of the C-terminal GST-specific all helical domain. Here we show that substitution of Ochrobactrum anthropi GST His15 and Glu198 with ala- nine greatly compromises the catalytic efficiency of the enzyme, even though none of these residues takes part to the enzyme active site. Thermal and chemical denaturation experiments point to a role for this network in global structure stabilization. Furthermore, we show that OaGST structure looses com- pactness at alkanine pHs and that this behavior may be ascribed to partial disruption of the H-bond net- work, pointing to an important role in zippering the N-terminal and C-terminal domains of the protein.