Lipid-protein Interactions in the Thylakoid Membranes of Higher Plant Chloroplasts

Abstract

The molecular organisation of the thylakoid membrane is usually described in terms of the fluid mosaic model. On this basis, the central matrix of the membrane is believed to consist of a fluid lipid bilayer. Membrane proteins are either attached to the surface of this bilayer by electrostatic forces or anchored within the bilayer by hydrophobic forces. A great deal of attention has been focussed on the spatial organisation of these protein components. Freeze-fracture studies have revealed the existence of large numbers of intra-membranous particles which can be characterised by their size, distribution between stromal and granal membranes, and the freeze-fracture faces with which they are associated (Staehelin et al. 1977; Arntzen 1978). Whilst there is still some debate regarding the origin of different groups of particles (Andersson, Anderson 1980), it is generally accepted that they reflect the presence of the chlorophyll-protein complexes of the two light-harvesting systems together with other intrinsic membrane proteins such as the cyt f / cyt b₆ complex and the CF₀ component of the coupling factor. Little or no attention, however, has been paid to the possible role of the membrane lipid fraction in thylakoid membrane organisation. This paper is directed at an examination of this problem.