Identification and role of the lipid binding site on light-harvesting complex II

Abstract

Formation of trimers of the light-harvesting complex II (LHCII) of plant thylakoid membranes is dependent on the presence of the lipid phosphatidylglycerol (PG) [1,2] and on the presence of certain conserved amino acid residues in the N-terminal [3] and C-terminal [4] region. Hobe et al. [3] presented hypothesis that region 16 – 21 is the PG binding site. LHCII is one of dominant phosphoproteins of thylakoids [5]. Phosphorylation site is located in the neighbourhood of the trimerisation site and is sequentially highly variable [6]. Upon phosphorylation of LHCII are exposed to solution aromatic amino acid sidechains [7] substantial part of which is located in the putative lipid binding site. The known structure of LHCII [8,9] does not give any details about the periphery of the extra-membrane domain where the N-terminus of LHCII extends. Jansson et al. [10] found that Lhcb2 subunits are more abundant in granal fractions than in stromal fractions. PG is more abundant than in photosystem II membranes than is its average concentration in thylakoids [11], while the distribution of other lipids is more or less uniform. Lipids together with LHCII cover most of the membrane surface and thus determine its properties. Subsequently, the surface properties determine both the adhesion of membrane lamellae and the separation of membrane fractions.