Membrane environment reduces the accessible conformational space available to an integral membrane protein

We studied the influence exerted on an integral membrane protein by its environment using the light-harvesting complex (LH1) of purple bacteria as a model. Single molecule spectroscopy of the LH1 bacteriochlorophyll pigments was used to compare membrane-reconstituted and detergent-solubilized complexes. The circular assemblies of the 32 bacteriochlorophyll a molecules present in the LH1 complex serve as a highly sensitive probe for protein deformation and disorder. It was shown that the membrane environment of the complex is essential for structural integrity, in particular, for conservation of the circular arrangement of pigments. We concluded that the membrane environment significantly narrows the statistical distribution of conformational states available to the LH1 complex in comparison to the corresponding state distribution observed for the same detergent-solubilized protein.