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Biochim Biophys Acta. 2009 Jun;1788(6):1332-40. doi: 10.1016/j.bbamem.2009.01.015. Epub 2009 Feb 3.

A giant liposome for single-molecule observation of conformational changes in membrane proteins.

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Department of Functional Molecular Science, The Graduate University for Advanced Studies (Sokendai), Okazaki, Aichi 444-8585, Japan.


We present an experimental system that allows visualization of conformational changes in membrane proteins at the single-molecule level. The target membrane protein is reconstituted in a giant liposome for independent control of the aqueous environments on the two sides of the membrane. For direct observation of conformational changes, an extra-liposomal site(s) of the target protein is bound to a glass surface, and a probe that is easily visible under a microscope, such as a micron-sized plastic bead, is attached to another site on the intra-liposomal side. A conformational change, or an angular motion in the tiny protein molecule, would manifest as a visible motion of the probe. The attachment of the protein on the glass surface also immobilizes the liposome, greatly facilitating its manipulation such as the probe injection. As a model system, we reconstituted ATP synthase (F(O)F(1)) in liposomes tens of mum in size, attached the protein specifically to a glass surface, and demonstrated its ATP-driven rotation in the membrane through the motion of a submicron bead.

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