Robert A. Niederman Professor Rutgers University Molecular Biology and Biochemistry Nelson Hall - Busch Campus. A317 Piscataway. NJ 08854 (732) 445-3985 FAX - 4213 rniederm@rci.rutgers.edu

Structure. function. and assembly of photosynthetic membranes

A variety of integrated biochemical. biophysical and molecular genetica approaches are used to investigate the structural organization and assembly of photosynthetic membranes in purple nonsulfur proteobacteria. an experimentally accessible prokaryotic model system. These membrane structures contain integral light-harvesting complexes which transfer excitations to photochemical reaction center. This initiates cyclic electron transfer through a mitochondrial-type cytochrome bc1 complex. resulting in re-reduction of the photooxidized reaction center and conservation of the light energy as an electrochemical proton gradient coupled to the synthesis of ATP.

The role which noncatalytic subunits play in electron transport complexes is being examined in the Rhodobacter sphaeroides cytochrome bc1 complex. which contains a unique polypeptide (subunit IV) lacking a prosthetic group. We have recently elucidated the membrane topology of this integral membrane protein and have constructed strains from which its structural gene has been deleted. This is serving as a basis for determining whether subunit IV is functionally essential. or has important structural and assembly roles. A second area of investigation involves elucidation of the structural basis for rapid and efficient excitation energy transfer by integral membrane light-harvesting complexes. The questions currently under investigation include: the nature of functionally crucial bacteriochlorophyll-protein and apoprotein associations in the peripheral light-harvesting proteins; the role of spectral heterogeneity in facilitating directed energy transfer from core light-harvesting complexes to the reaction center; determining how singlet excitation energy transfer from carotenoids to bacterioclorophyll competes with deexcitation processes; and the role which an open reading frame (pufX). located immediately downstream from genes encoding core light-harvesting and reaction center polypeptides. plays in the organization of photosynthetic units.

Selected Publications

Sturgis JN, Tucker JD, Olsen JD, Hunter CN, Niederman RA. (2009) Atomic force microscopy studies of native photosynthetic membranes. Biochemistry. 48(17):3679-98.

Sturgis JN, Niederman RA. (2008) Atomic force microscopy reveals multiple patterns of antenna organization in purple bacteria: implications for energy transduction mechanisms and membrane modeling. Photosynth Res. 95(2-3):269-278.

Georgakopoulou S. van der Zwan G. Olsen JD. Hunter CN. Niederman RA. van Grondelle R. (2006) Investigation of the effects of different carotenoids on the absorption and CD signals of light harvesting 1 complexes. J Phys Chem B Condens Matter Mater Surf Interfaces Biophys. 110(7):3354-61.

Hunter CN. Tucker JD. Niederman RA. (2005) The assembly and organisation of photosynthetic membranes in Rhodobacter sphaeroides. Photochem Photobiol Sci. 4(12):1023-7.

Koblízek. M.. Shih. J.D.. Breitbart. S.I.. Ratcliffe. E.C.. Kolber. Z.S.. Hunter. C.N. and Niederman. R.A. (2005) Sequential assembly of photosynthetic units in Rhodobacter sphaeroides as revealed by fast repetition rate analysis of variable bacteriochlorophyll a fluorescence. Biochim. Biophys. 1706(3):220-31.

Frese. R.N. Siebert. C.A.. Niederman. R.A.. Hunter. C. N.. Otto. C. and van Grondelle. R. (2004) The long-range organization of a native photosynthetic membrane. Proc. Natl. Acad. Sci. USA 101:17994-17999.

Bahatyrova. S.. Frese. R.N.. Siebert. C.A.. van der Werf. K.O.. van Grondelle. R.. Niederman. R.A.. Bullough. P.A.. Otto. C. Olsen. J.D. and Hunter. C.N. (2004) The native architecture of a photosynthetic membrane. Nature 430:1058-1062.

Papagiannakis. E.. van Stokkum. I.H.M.. van Grondelle. R.. Niederman. R.A.. Zigmantas. D.. Sundström. V.and Polívka. T. (2003) A near-infrared transient absorption study of the excited state dynamics of the carotenoid spirilloxanthin in solution and in the LH1 complex of Rhodospirillum rubrum. J. Phys. Chem. B 107:11216-11223.

Westerhuis. W. H. J.. Sturgis. J. N.. Ratcliffe. E. C.. Hunter. C. N. and Niederman. R. A. (2002) Isolation. size estimates and spectral heterogeneity of an oligomeric series of light-harvesting 1 complexes from Rhodobacter sphaeroides. Biochemistry 41:8698-8707.

Drews. G. and Niederman. R. A. (2002) Membrane biogenesis in anoxygenic photosynthetic prokaryotes. Historical Minireview for "History of Photosynthesis: A Celebration of the Millennium." Photosynth. Res. 73:87-94.

Gradinaru. C.C.. Kennis. J.T.M.. Papagiannakis. E.. van Stokkum. I.H.M.. Cogdell. R.J.. Fleming. G.R.. Niederman. R.A. and van Grondelle. R. (2001) An unusual pathway of excitation energy deactivation in carotenoids: singlet-to-triplet conversion on an ultrafast time scale in a photosynthetic antenna. Proc. Natl. Acad. Sci. USA 98:2364-2369.