Spectroscopic Analyses of Manganese Ions Effects on the Conformational Changes of Inorganic Pyrophosphatase from Psychrophilic Shewanella sp. AS-11
Mn2+ ions influence the activity, temperature dependence, and thermostability of the psychrophilic Shewanella-PPase (Sh-PPase), and are required to function in cold environments. The functional characteristics of Sh-PPase on activation with Mn2+ ions are possibly related to conformational changes in the molecule. In this study, conformational changes of Sh-PPase on activation with Mn2+ ions were analyzed in solution by fluorescence spectroscopy analysis of intrinsic tryptophan residues, 1-anilino-8-naphthalene sulfonate fluorescence, and circular dichroism spectroscopy. For Sh-PPase, Mn2+ ions did not affect the flexibility of the tryptophan residues and secondary structure of the enzyme. However, the microenvironment of the tryptophan residues and surface area of Sh-PPase were more hydrophilic on activation with Mn2+ ions. These results indicate that activation with Mn2+ ions causes conformational changes around the aromatic amino acid residues and affects the hydrophobicity of the enzyme surface, which results in conformational changes. Substrate-induced conformational changes reflect that metal-free Sh-PPase in solution indicated an open structure and will be a close structure when binding substrate. In combination of our spectroscopic analyses on Sh-PPase, it can be concluded that activation with Mn2+ ions changes some conformation of Sh-PPase molecule in solution.