LHCII is the most abundant membrane protein on earth. It participates in the 
first steps of photosynthesis by harvesting sunlight and transferring excitation 
energy to the core complex. Here we have analyzed the LHCII complex of the green 
alga Chlamydomonas reinhardtii and its association with the core of Photosystem 
II (PSII) to form multiprotein complexes. Several PSII supercomplexes with 
different antenna sizes have been purified, the largest of which contains three 
LHCII trimers (named S, M and N) per monomeric core. A projection map at a 13Å 
resolution was obtained allowing the reconstruction of the 3D structure of the 
supercomplex. The position and orientation of the S trimer are the same as in 
plants; trimer M is rotated by 45° and the additional trimer (named here as 
LHCII-N), which is taking the position occupied in plants by CP24, is directly 
associated with the core. The analysis of supercomplexes with different antenna 
sizes suggests that LhcbM1, LhcbM2/7 and LhcbM3 are the major components of the 
trimers in the PSII supercomplex, while LhcbM5 is part of the "extra" LHCII pool 
not directly associated with the supercomplex. It is also shown that 
Chlamydomonas LHCII has a slightly lower Chlorophyll a/b ratio than the complex 
from plants and a blue shifted absorption spectrum. Finally the data indicate 
that there are at least six LHCII trimers per dimeric core in the thylakoid 
membranes, meaning that the antenna size of PSII of C. reinhardtii is larger 
than that of plants.