Switching light harvesting complex II into photoprotective state involves the lumen-facing apoprotein loop

Area of Science:

• Plant Biology
• Photosynthesis Research
• Biophysics

Background:

• High light conditions activate non-photochemical quenching (NPQ) in plants for photoprotection.
• The major light harvesting complex (LHCII) is crucial for NPQ, with spectral changes suggesting conformational shifts.

Purpose of the Study:

• To investigate the role of specific amino acid residues in the lumenal loop of LHCII.
• To understand how mutations affect LHCII's pH sensitivity and quenching capacity.
• To explore potential manipulation of light harvesting efficiency.

Main Methods:

• Site-directed mutagenesis of recombinant LHCII complexes.
• Analysis of quenching capacity under varying pH conditions.
• Spectroscopic measurements including fluorescence lifetime and 77 K fluorescence spectroscopy.

Main Results:

• Mutating aspartate 111 (D111) to valine (V111) increased quenching capacity under low pH by shifting the pK.
• This D111 mutation correlated with a 40% reduction in fluorescence lifetime and a lower energy emitting state.
• Mutating glutamate 94 (E94) to glycine (G94) reduced fluorescence quenching yield at low pH.

Conclusions:

• Subtle changes in LHCII apoprotein structure via single amino acid mutagenesis significantly alter pH sensitivity and NPQ establishment.
• This study provides insights into the molecular mechanisms of NPQ.
• The findings suggest potential for engineering light harvesting complexes for hybrid energy systems.