Effects of heat treatment on the protein secondary structure and pigment microenvironment in photosystem 1 complex

Abstract

The protein secondary structure and pigments' microenvironment in photosystem 1 (PS1) complexes were studied in the temperature range of 25-80 o C using Fourier transform infrared (FT-IR) and circular dichroism (CD) spectroscopy, respectively. Quantitative analysis of the component bands of the amide I band (1 700-1 600 cm -1 ) showed no significant change below 50 o C. However, apparent conformational changes occurred at 60 o C and further continued at 70 and 80 o C accompanied with transitions of secondary structure mainly from α-helix to the β-sheet structures. CD analysis demonstrated that the regular arrangement, viz. protein microenvironment of pigments of PS1 complexes, was destroyed by heat treatment which might come from the changes of protein secondary structure of PS1. The CD signals at 645 nm contributed by chlorophyll (Chl) b of light-harvesting complex 1 (LHC1) were easily destroyed at the beginning of heat treatment (25-60 o C). When temperature reached 70 and 80 o C, the CD signals at 478 nm contributed mainly by Chl b of LHC1 and 498 nm contributed by carotenoids decreased most rapidly, indicating that LHC1 was more sensitive to high temperature than core complexes. In addition, the oxygen uptake rate decreased by 90.81 % at 70 o C and was lost completely at 80 o C showing that heat treatment damaged the regular function of PS1 complexes. This may be attributed to heat-induced changes of pigment microenvironment and protein secondary structure, especially transmembrane α-helix located in PsaA/B of PS1.

Effects of ethanol treatment on rheological and gel properties of chicken myofibrillar protein

“…The same trend was found in heating egg white protein (Seguchi et al, 2004). Hu, Xu, Gong, and Kuang (2005) also found an apparent convert of photosystem I in which the α-helix is converted to β-sheet during 60°C to 80°C. The decrease of α-helix represented an increase in unfolding protein molecules and a decrease in intermolecular hydrogen bonds in peptide chains.…”

Stimulus-responsive light-harvesting complexes based on the pillararene-induced co-assembly of β-carotene and chlorophyll

“…4e ). 53 In addition, visible CD spectroscopy is a sensitive technique to monitor excitonic pigment–pigment and pigment–protein interactions 54 . As shown in Supplementary Fig.…”

Tolerance of the widespread cyanobacterium Nostoc commune to extreme temperature variations (−269 to 105°C), pH and salt stress

“…Dry inactive specimens of N. commune also show signs of denaturation above 80°C, and they are as equally sensitive as rewetted active specimens. The regular protein-pigment structure of the photosystem I complexes of closely related N. flagelliforme has also been reported to be destroyed by heat treatment at 70 and 80°C (Hu et al 2005). Mixed photosynthetic communities are present below rock surfaces on savannas, deserts and semi-deserts of arctic and subtropical regions and show desiccation and temperature tolerance resembling that of N. commune.…”