Molecular dissection of the soluble photosynthetic antenna from a cryptophyte alga

Cryptophyte algae have a unique phycobiliprotein light-harvesting antenna that fills a spectral gap in chlorophyll absorption, however, it is unclear how it transfers energy efficiently to photosystems. We show that the cryptophyte Hemiselmis andersenii expresses an energetically complex antenna comprising three distinct spectrotypes of phycobiliprotein with different quaternary structures arising from a diverse α subunit family. The bulk of the antenna consists of open quaternary form phycobiliproteins acting as primary photon acceptors, supplemented by novel open-braced forms. The final components are closed forms with a long wavelength spectral feature due to substitution of a single chromophore. We propose that the macromolecular organization of the cryptophyte antennas consists of bulk open and open-braced forms that transfer excitations to photosystems via this bridging closed form phycobiliprotein.