Secondary structure and thermostability of the photosystem II manganese-stabilizing protein of the thermophilic cyanobacterium Synechococcus elongatus

Abstract

The secondary structure of the manganese-stabilizing protein of the thermophilic cyanobacterium Synechococcus elongatus in solution was investigated by Fourier-transform infrared (FT-IR) and circular dichroism (CD) spectroscopies. Both methods showed a high proportion of disordered structure (40–43%) and a relatively small amount of β-sheet (23–24%) and α-helix (17–19%). The conformation of the protein remained essentially unchanged at temperatures up to 70°C. Unfolding of the protein occurred at higher temperatures and FT-IR spectroscopy revealed that β-sheet was more strongly unfolded than α-helix at 76°C. The protein largely lost the ordered secondary structures at 90°C, but, when cooled down to 30°C, regained its original conformation. Thus, the cyanobacterial protein is very thermostable and its denaturation at an extremely high temperature is reversible.