Tuning of the Chl and Chl properties in photosystem II by site-directed mutagenesis of neighbouring amino acids.

Photosystem II is the water/plastoquinone photo-oxidoreductase of photosynthesis. The photochemistry and catalysis occur in a quasi-symmetrical heterodimer, D1D2, that evolved from a homodimeric ancestor. Here, we studied site-directed mutants in PSII from the thermophilic cyanobacterium Thermosynechoccocus elongatus, focusing on the primary electron donor chlorophyll a in D1, Chl, and on its symmetrical counterpart in D2, Chl, which does not play a direct photochemical role.

New insights on Chl function in Photosystem II from site-directed mutants of D1/T179 in Thermosynechococcus elongatus.

The monomeric chlorophyll, Chl, which is located between the PP chlorophyll pair and the pheophytin, Pheo is the longest wavelength chlorophyll in the heart of Photosystem II and is thought to be the primary electron donor. Its central Mg is liganded to a water molecule that is H-bonded to D1/T179. Here, two site-directed mutants, D1/T179H and D1/T179V, were made in the thermophilic cyanobacterium, Thermosynechococcus elongatus, and characterized by a range of biophysical techniques.