Abstract:
The conversion of solar radiation to chemical
energy in plants and green algae takes place in the thylakoid
membrane. This amphiphilic environment hosts a
complex arrangement of light-harvesting pigment-protein
complexes that absorb light and transfer the excitation
energy to photochemically active reaction centers. This
efficient light-harvesting capacity is moreover tightly
regulated by a photoprotective mechanism called nonphotochemical
quenching to avoid the stress-induced
destruction of the catalytic reaction center. In this review
we provide an overview of single-molecule fluorescence
measurements on plant light-harvesting complexes
(LHCs) of varying sizes with the aim of bridging the gap
between the smallest isolated complexes, which have
been well-characterized, and the native photosystem. The
smallest complexes contain only a small number (10–20)
of interacting chlorophylls, while the native photosystem
contains dozens of protein subunits and many hundreds
of connected pigments. We discuss the functional significance
of conformational dynamics, the lipid environment, and the structural arrangement of this fascinating nanomachinery.
The described experimental results can be
utilized to build mathematical-physical models in a bottom-
up approach, which can then be tested on larger in
vivo systems. The results also clearly showcase the general
property of biological systems to utilize the same system
properties for different purposes. In this case it is the regulated
conformational flexibility that allows LHCs to switch
between efficient light-harvesting and a photoprotective
function.
