Structural and conformational behavior of MurE ligase from Salmonella enterica serovar Typhi at different temperature and pH conditions.

MurE ligase is known to play a significant role in peptidoglycan biosynthesis. It catalyzes the addition of meso-diaminopimelic acid to nucleotide precursor. The protein can adopt different conformations for its proper functioning. Different environmental conditions can alter the stability and function of enzyme due to their ability to disrupt interactions between different domains. We have explored the pH and temperature dependent conformational changes in MurE ligase from Salmonella Typhi and estimated the protein stability. The study enabled us to decipher the effect of different milieu condition in the enzyme activity. At acidic pH 3.0, StMurE ligase forms molten globule (MG) state and at alkaline pH it is in unfolded state. The different states of StMurE ligase were characterized using various spectroscopic techniques. These techniques including near-UV CD, far-UV CD, ANS fluorescence, differential scanning calorimetry and fluorescence spectroscopy helped to determine the secondary structural changes and detect local conformational modifications. The structural analysis using StMurE ligase homology model revealed the variations in ionization states of catalytic amino acid residues involved in substrate binding. This study provides an insight into the dynamics states of StMurE ligase at different environmental conditions during bacterial pathogenesis.