Phycobilisomes are protein complexes that harvest light and transfer energy to the photo system. Here, the three dimensional structure of intact phycobilisomes from Nostoc flagelliforme is studied by a combination of negative stain electron microscopy and cryo-electron microscopy. Results show that the intact phycobilisomes are composed of a tricylindrical core and six rods. Each allophycocyanin cylinder presents a double-layered structure when viewed from the side and a triangular shape when viewed from the top. These characteristics indicate that allophycocyanin trimers in the intact phycobilisomes are arranged into hexameric oligomers in a parallel manner.
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