(582ba) Understanding the Functional Oligomerization State of Peridinin-Chlorophyll a-Proteins in the Dinoflagellate Symbiodinium

Jiang, J., Washington University
Zhang, H., Washington University in St. Louis
Blankenship, R., Washington University in St. Louis
Lo, C. S., Washington University in St. Louis

Symbiodinium is the most commonly found group of endosymbiotic dinoflagellates in corals. Peridinin-chlorophyll a-proteins (PCP) are one of the major light harvesting complexes in photosynthetic dinoflagellates. The X-ray crystal structure of MFPCP (main form PCP) of Amphidinium carterae has revealed a trimer [1], while HSPCP (high-salt form PCP) from the same strain and recombinant PCP crystallized as monomers [2, 3]. It is still unclear, whether the trimer of Amphidinium carterae MFPCP is an exception, or trimerization is common among PCPs. Our study utilized native mass spectrometry, gel filtration chromatography, chemical cross-linking and small-angle neutron scattering (SANS) to reveal the functional oligomerization state(s) of PCP in the dinoflagellate Symbiodnium. We found that most PCP in aqueous buffer is monomeric, with the presence of a small amount of trimeric PCP. We conclude that PCP monomer is able to fulfill its function, e.g. light-harvesting, but the oligomerization states in vivo remains to be understood.

[1] E. Hofmann, P.M. Wrench, F.P. Sharples, R.G. Hiller, W. Welte, K. Diederichs, Structural basis of light harvesting by carotenoids: peridinin-chlorophyll-protein from Amphidinium carterae, Science, 272 (1996) 1788-1791.

[2] T. Schulte, F.P. Sharples, R.G. Hiller, E. Hofmann, X-ray structure of the high-salt form of the peridinin-chlorophyll a-protein from the dinoflagellate Amphidinium carterae: modulation of the spectral properties of pigments by the protein environment, Biochemistry, 48 (2009) 4466-4475.

[3] T. Schulte, D.M. Niedzwiedzki, R.R. Birge, R.G. Hiller, T. Polivka, E. Hofmann, H.A. Frank, Identification of a single peridinin sensing Chl-a excitation in reconstituted PCP by crystallography and spectroscopy, Proc Natl Acad Sci U S A, 106 (2009) 20764-20769.