Structural Basis of Light Harvesting by Carotenoids: Peridinin-Chlorophyll-Protein from

Peridinin-chlorophyll-protein, a water-soluble light-harvesting complex that has a blue-green absorbing carotenoid as its main pigment, is present in most photosynthetic dinoflagellates. Its high-resolution (2.0 angstrom) x-ray structure reveals a noncrystal-lographic trimer in which each polypeptide contains an unusual jellyroll fold of the a-helical amino- and carboxyl-terminal domains. These domains constitute a scaffold with pseudo-twofold symmetry surrounding a hydrophobic cavity filled by two lipid, eight peridinin, and two chlorophyll a molecules. The structural basis for efficient excitonic energy transfer from peridinin to chlorophyll is found in the clustering of peridinins around the chlorophylls at van der Waals distances. Table 1. Crystallographic data. Data collection: Native1 and derivative data (5 IllM K2 PtCI4, 1-day soak) were collected on a rotating anode source (CuKa, 40 kV, 100 mA) with a STOE (Darmstadt, Germany) imaging plate detector. Native2 was collected at the BW7B wiggler bealllline at DESY on a 30-cm MARresearch (Hamburg, Germany) image plate. All data were processed with XDS (26). Phasing: Six heavy-atom binding sites were found using SHELXS (27) in Patterson search mode, and four additional sites were found by inspection of difference Fourier maps. Refinement of heavy-atom parameters wa