A quantitative analysis of protein secondary structure of photosystem II particles and light-harvesting complex of chloroplast thylakoid membranes by FT-IR spectroscopy

Abstract

We report the preliminary results of protein conformational analysis of photosystem II (PSII) particles and light-harvesting complex (LHC-II) of chloroplast thylakoid membranes isolated from fresh spinach in aqueous solution at neutral pH. FT-IR spectroscopy, with its self-deconvolution and second derivative resolution enhancement as well as curve-fitting procedures, was used in the amide I region (1700−1600 cm−1), to determine the amount of each conformation present in coexistence.Spectroscopic data have shown the domination of the α-helix (1656 cm−1) to be a major conformational component in both PSII (64%) and LHC-II (48%) systems. The β-sheet (1626–1640 cm−1), with 17% for PSII and 21% for LHC-II, and the turn structure (1670–1680 cm−1), with 23% for LHC-II and 13% for PSII, with β-antiparallel (1689–1691 cm−1) 8% for LHC-II and 6% for PSII, were the minor conformations present in aqueous solution.