Expression of membrane-bound iron-sulfur proteins.

Overexpression of membrane-bound proteins to obtain milligram quantities for biochemical and biophysical studies is usually a difficult task, especially for those proteins that span the membrane several times (3). An additional difficulty arises when these proteins need to incorporate organic or inorganic cofactors. In order to obtain a functional protein, this requires a host that is able to produce this cofactor or the cofactor has to be added to the growth medium and subsequently taken up by the host cells. Alternatively, the protein can be expressed as inclusion bodies and then refolded in the presence of the cofactor(s), a strategy successfully applied for bacteriorhodopsin and the light-harvesting complex of higher plants (3).