Phycobilisome, cyanobacteria light harvesting complex, shows an uneven bottom surface, in contrast to the flat, reducing side of photosystem II (PSII) for good.

It’s long been thought that the two basal cylinders of a phycobilisome adopt an antiparallel configuration, sitting on the flat reducing side of a PSII dimer, leaving no space, which is beneficial to efficient energy transfer from terminal energy emitters on each basal cylinder to the chlorophylls in PSII. This video clip shows an alternative senario that, without compromising efficient energy transfer from phycobilisome to PSII, two basal cylinders make an acute angel (side view, cylinders parallel to the screen) with two protrusion domains formed by ApcE PB domain and ApcD biting into the reducing side of a PSII and two distal discs in each cylinder tilting up away from the flat surface of PSII, from a recent publication 2021.