Interaction of monogalactosyldiacylglycerol with cytochrome b₆f complex in surface films.

The interaction of monogalactosyldiacylglycerol (MGDG) with cytochrome b(6)f complex (cyt b(6)f), a major component of the photosynthetic apparatus, was studied in Langmuir monolayers during compression/expansion cycling and at constant surface pressure mode. The surface pressure/area isotherms of the mixed films were analyzed in terms of surface compressional modulus and two-dimensional virial equation of state. The morphology and the surface potential of the monolayers were monitored by Brewster angle microscopy and vibrating plate sensor respectively. Our results suggested that there is a specific interaction between MGDG and cyt b(6)f which resulted in depletion of lipid molecules from the interface. The current work sheds light on the still unclear question how b(6)f complex gets in touch with the major compound of the thylakoid membranes, the non-charged lipid MGDG. The interaction occured even at very low sub-nanomolar concentration of the complex. This effect most probably could be attributed to hydrogen bonding between the galactose headgroup of the lipid and the protein moiety of cyt b(6)f.