The unusual light-harvesting complex of Mantoniella squamata: supramolecular composition and assembly.

The supramolecular properties of the chlorophyll a/b/c light-harvesting protein complex of Mantoniella squamata were analyzed. The complex is built up of at least two subunits of M(r) 20,000 and 22,000, which are encoded in the nucleus as precursor proteins of M(r) 27,000. The chlorophyll a/b/c light-harvesting complex is the dominating protein of the thylakoids and is fractured with the protoplasmic membrane face as a 7.5 nm particle. These particles form paracrystalline arrays with a purported hexagonal arrangement in native thylakoids and form similar arrays when reconstituted in liposomes. The light-harvesting complexes are supposed to be trimers with a trigonal arrangement of the subunits. Preliminary amino acid sequence data show that the chlorophyll a/b/c light-harvesting complex of M. squamata is more related to the chlorophyll a/b complex of higher plants than to the light-harvesting complexes of chromophytan algae.