The ATP binding cassette transporters epitomize nature's ability to re-use a successful protein motif. With diverse membrane-spanning regions, but highly conserved soluble ATP binding domains, the ABC transporters serve a wide variety of functions and are defunct in disorders such as Tangier disease and cystic fibrosis (see All in the Superfamily). Small wonder then, that the first high-resolution structures of this largest family of transporters were greeted with great acclaim. But there was puzzlement as well; the structures did not agree. "The initial MsbA structure came as a surprise ... although it was undoubtedly the result of an impressive tour de force," writes Kaspar Locher, of the Swiss Federal Institute of Technology in an E-mail interview.
In the first of this issue's Hot Papers, Geoffrey Chang and Christopher Roth of the Scripps Research Institute, La Jolla, Calif., crystallized a lipid exporter known as MsbA from Escherichia coli.1 MsbA facilitates the ...
