Protein secondary structure of the isolated photosystem II reaction center and conformational changes studied by Fourier transform infrared spectroscopy

Abstract

The secondary structure of the photosystem II (PSII) reaction center isolated from pea chloroplasts has been characterized by Fourier transform infrared (FTIR) spectroscopy. Spectra were recorded in aqueous buffers containing H2O or D2O; the detergent present for most measurements was dodecyl maltoside. The broad amide I and amide II bands were analyzed by using second-derivative and deconvolution procedures. Absorption bands were assigned to the presence of alpha-helices, beta-sheets, turns, or random structure. Quantitative analysis revealed that this complex contained a high proportion of alpha-helices (67%) and some antiparallel beta-sheets (9%) and turns (11%). An irreversible decrease in the intensity of the band associated with the alpha-helices occurs upon exposure of the isolated PSII reaction center to bright illumination. This loss of alpha-helical content gave rise to an increase in other secondary structures, particularly beta-sheets. After similar pretreatment with light, sodium dodecyl sulfate polyacrylamide gel electrophoresis reveals lower mobility and solubility of constituent D1 and D2 polypeptides of the PSII reaction center. Some degradation of these polypeptides also occurs. In contrast, there is no change in the mobility of the two subunits of cytochrome b559. In the absence of illumination, the PSII reaction center exchanged into dodecyl maltoside shows good thermal stability as compared with samples in Triton X-100. Only at a temperature of about 60 degrees C do spectral changes take place that are indicative of denaturation.

Thermal stabilization of a single‐chain Fv antibody fragment by introduction of a disulphide bond

“…Upon he.tting all three samples, a gradual increase in the intensity of tht 1635 cm -~ vibration was observed, concomitant with increases at 1690 and 1620 cm -1. The latter changes have been no~ ed previously in thermal denaturation spectra and are attribuled to protein aggregation [19,20]. The thermal denaturation cmves obtained from the changes in intensity at 1620 cm -~ are shown in Fig.…”

Conversion of alpha-helices into beta-sheets features in the formation of the scrapie prion proteins.

“…Examples of other proteins with a-helices that are converted into p-sheets and vice versa include the photosystem II reaction center, which exhibits an a-helix 4 p-sheet transition when exposed to light (54) Serpin proteins, in which a (3sheet is transformed into an a-helix upon proteolytic activation (56). In Alzheimer disease, amyloid plaques contain 13A4 peptide which is derived from amyloid precursor protein (p-APP) that seems to undergo a similar structural transition.…”

Complexation of Heavy Metal Cations Hg, Cd, and Pb with Proteins of PSII: Evidence for Metal–Sulfur Binding and Protein Conformational Transition by FTIR Spectroscopy

“…The high toxicity of Cd ion for plants is tle structural changes associated with the metal ion binding well known; it is also shown that the Cd cation inhibits site and the quantitative analysis of protein conformation, photosynthetic electron transport and the activity of the PSII, even in a large protein complex such as PSII reaction cenaffecting the water splitting and oxygen evolution (2). Simi-ter ( 15,16 ) . larly, the Pb ion inhibition of the PSII reaction center in…”