Crystal Structure of the Membrane Fusion Protein CusB from Escherichia coli

Journal Article · Mon Mar 29 04:00:00 EDT 2010 · J. Mol. Biol.

DOI:https://doi.org/10.1016/j.jmb.2009.08.029· OSTI ID:1006036

Su, Chih-Chia; Yang, Feng; Long, Feng; Reyon, Deepak; Routh, Mathew D; Kuo, Dennis W; Mokhtari, Adam K; Van Ornam, Jonathan D; Rabe, Katherine L; Hoy, Julie A; Lee, Young Jin; Rajashankar, Kanagalaghatta R; Yu, Edward W

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 Laboratory (ANL)
• Sponsoring Organization: USDOE
• OSTI ID: 1006036
• Journal Information: J. Mol. Biol., Journal Name: J. Mol. Biol. Journal Issue: (2) ; 10, 2009 Vol. 393; ISSN JMOBAK; ISSN 0022-2836
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

36 MATERIALS SCIENCE
ARCHITECTURE
BACTERIA
CRYSTAL STRUCTURE
ESCHERICHIA COLI
MEMBRANES
MONOCRYSTALS
PROTEINS
SUBSTRATES
TRANSPORT