Crystal Structure of the Membrane Fusion Protein CusB from Escherichia coli
Gram-negative bacteria, such as Escherichia coli, frequently utilize tripartite efflux complexes belonging to the resistance-nodulation-division family to expel diverse toxic compounds from the cell. These systems contain a periplasmic membrane fusion protein (MFP) that is critical for substrate transport. We here present the x-ray structures of the CusB MFP from the copper/silver efflux system of E. coli. This is the first structure of any MFPs associated with heavy-metal efflux transporters. CusB bridges the inner-membrane efflux pump CusA and outer-membrane channel CusC to mediate resistance to Cu{sup +} and Ag{sup +} ions. Two distinct structures of the elongated molecules of CusB were found in the asymmetric unit of a single crystal, which suggests the flexible nature of this protein. Each protomer of CusB can be divided into four different domains, whereby the first three domains are mostly {beta}-strands and the last domain adopts an entirely helical architecture. Unlike other known structures of MFPs, the {alpha}-helical domain of CusB is folded into a three-helix bundle. This three-helix bundle presumably interacts with the periplasmic domain of CusC. The N- and C-termini of CusB form the first {beta}-strand domain, which is found to interact with the periplasmic domain of the CusA efflux pump. Atomic details of how this efflux protein binds Cu{sup +} and Ag{sup +} were revealed by the crystals of the CusB-Cu(I) and CusB-Ag(I) complexes. The structures indicate that CusB consists of multiple binding sites for these metal ions. These findings reveal novel structural features of an MFP in the resistance-nodulation-division efflux system and provide direct evidence that this protein specifically interacts with transported substrates.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 1006036
- Journal Information:
- J. Mol. Biol., Vol. 393, Issue (2) ; 10, 2009; ISSN 0022-2836
- Country of Publication:
- United States
- Language:
- ENGLISH
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