Crystal structure of the CusBA heavy-metal efflux complex of Escherichia coli

Gram-negative bacteria expel toxic chemicals through tripartite efflux pumps spanning both the inner and outer membranes. A crystallographic model of this tripartite efflux complex has been unavailable because co-crystallization of different components of the system has proved extremely difficult. The X-ray crystal structure of the CusA/CusB co-complex from Escherichia coli has now been determined. The structure reveals that the trimeric CusA efflux pump interacts with six CusB protein molecules at the upper half of the periplasmic domain, and the predicted structure of the trimeric CusC channel was used to develop a model of the tripartite efflux complex.