Effects of a non-ionic detergent on the spectral properties and aggregation state of the light-harvesting chlorophyll a/b protein complex (LHCII)

The dependence of the spectroscopic properties and aggregation state of a highly purified light-harvesting chlorophyll a/b protein complex (LHCII) population on detergent (octyl-β-d-glucopyranoside (OGP)) concentration in the solvent was investigated. The results, including circular dichroism, time-resolved fluorescence, sucrose gradient centrifugation and isoelectrofocusing, indicate that, depending on the detergent concentration, LHCII can be found in two main quaternary states whose minimal order is three. Thus, at high OGP concentrations (3% or greater), a trimer, which is identical with the trimeric form observed in two-dimensional crystals, is stable. At OGP concentrations lower than approximately 0.65%, macroscopic aggregates are formed, accompanied by the appearance of strong pigment-pigment interactions and fluorescence quenching. At intermediate OGP concentrations (0.650%-2%) an oligomeric form of LHCII, possibly a multiple of the trimer, is stable and is similar to the so-called CPII′ oligomeric form resolved by non-denaturing sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE).