Effect of biogenic polyamine spermine on the structure and function of photosystem I
•The binding sites of spermine with PSI reaction center were located.•Spermine induced major conformational changes without altering PSI activity.•Polyamine interaction provides protection for the PSI under high light stress.•The major structural modifications induced by spermine is on the proteins of the PSI electron donor side.
We located the binding sites of spermine (Spm) to PSI sub-membrane proteins and the impact of this interaction on the photoprotection of PSI activity, using spectroscopic methods and molecular modeling. Our results showed that at high Spm content the polyamine binds PSI polypeptides through H-bonding and induces major protein conformational changes with the reduction of α-helix from 52% to 42% and an increase of the β-sheet from 26% to 29%. However, polyamine does not affect significantly the photooxidizable P700 in control sample and considerably protects it against strong illumination. On the contrary, protein conformational changes coincide with an important inhibition of O2 uptake rates by polyamine, which revealed that the protein of the PSI donor side plastocyanin is a main target for Spm inhibition. The photoprotection of PSI photochemical activity may be due to the stabilization of the PSI stromal polypeptides by Spm as shown by the docking results. Spm binds to different amino acids with hydrophilic and hydrophobic characters, while the presence of several H-bondings stabilizes Spm–PSI complexation.
Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide
Journal: Journal of Photochemistry and Photobiology B: Biology - Volume 141, December 2014, Pages 76–83