Figure 1.

Crystal structures of the CusB and CusA efflux proteins. (a) Ribbon diagram of the CusB protomer. The structure can be divided into four distinct domains. Domain 1 (red) is formed by the N- and C-termini and is located above the inner membrane. The loops between domains 2 (blue) and 3 (magenta) appear to form an effective hinge to allow the molecule to shift from an open conformation to a more compact structure. Domain 4 (green) is folded into an anti-parallel, three-helix bundle, which is thought to be located near the outer membrane. (b) Ribbon diagram of the CusA protomer viewed in the membrane plane. Sub-domains DN, DC, PN1, PN2, PC1 and PC2 are coloured cyan, magenta, yellow, orange, green and red, respectively. The transmembrane helices are coloured blue. (c) Ribbon diagram of the CusA homotrimer viewed in the membrane plane. Each subunit of CusA is labelled with a different colour. Sub-domains DN, DC, PN2, PC1 and PC2 are labelled on the front protomer (magenta). The location of PN1 in this protomer is behind PN2, PC1 and PC2 (see text).