Chloroplast light-harvesting complex II holds half of the chlorophyll in nature, and therefore harvests half of the sunlight that is converted in photosynthesis. This pigment-protein complex is embedded in the chloroplast thylakoid membrane.
The graphic is produced from atomic coordinates kindly provided by Dr W. Kuehlbrandt. It shows a view of the polypeptide chain of the complex. The initial view is parallel to the membrane plane. Chlorophyll and carotenoid molecules are blue. The polypeptide chain varies in colour from the amino-terminus (blue) to the carboxy-terminus (red). From the amino-terminal end of the polypeptide, at the top of the picture, the polypeptide chain passes through the membrane as a long helix. The chain passes back through the membrane as a shorter helix, then back again as a third, long helix. A fourth, short helix runs along the inner surface of the membrane. Only helices and pigment molecules are available in the coordinate file.
The amino-terminus, exposed at the outer surface of the membrane, contains the site of phosphorylation. We have shown that phosphorylation regulates the function of the complex by altering its structure. Kinemages of the light-harvesting complex and of the phosphorylated amino-terminus are available. An animation of a possible structure at the amino-terminus of the phosphorylated protein is also presented with its atomic coordinates.