Secondary structure and thermal stability of the extrinsic 23 kDa protein of photosystem II studied by Fourier transform infrared spectroscopy

摘要

>The secondary structure and thermal stability of the extrinsic 23 kDa protein (OEC23) of spinach photosystem II have been characterized in solution between 25 and 75°C using Fourier transform infrared spectroscopy. Quantitative analysis of the amide I band (1700–1600 cm−1) shows that OEC23 contains 5% α-helix, 37% β-sheet, 24% turn, and 34% disorder structures at 25°C. No appreciable conformational changes occur below 45°C. At elevated temperatures, the β-sheet structure is unfolded into the disorder structure with a major conformational transition occurring at 55°C. Implications of these results for the functions of OEC23 in photosystem II are discussed.