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1	Characterization of the Interactions Mediated by the Key Structural Protein CcmL: Cornerpiece of the Beta-Carboxysome Keeling, Thomas 16 January 2013 (has links) While much is known about the structure and interactions of the β-carboxysomal proteins, interactions of the proposed vertex protein CcmL with the other components have not yet been directly demonstrated. A fluorescence resonance energy transfer based method combined with other complementary spectrophotometry techniques as well as x-ray crystallography and transmission electron microscopy was used in a Thermosynechococcus elongatus BP-1 model to study these interactions. CcmL was found to interact with the various CcmK shell proteins with a clear binding preference for CcmK2; the previously proposed interaction of CcmL with CcmM was shown to not occur in vitro, and a possible CcmL-CcmL interaction was observed tentatively. In addition, analysis of a novel x-ray crystal structure of Nostoc sp. PCC7120 CcmL in a decameric form suggests a possibility of a CcmL-CcmL back-to-back interaction. This study gives the first direct experimental evidence for the biological role of CcmL as the carboxysomal vertex protein. carboxysome protein cyanobacteria fluorescence electron microscopy FRET x-ray crystallography protein interaction tryptophan fluorescence bacterial microcompartment dynamic light scattering Thermosynechococcus elongatus Nostoc sp. PCC7120 fluorescence resonance energy transfer