title: Evidence for the requirement of CydX in function but not assembly of the cytochrome bd oxidase in Shewanella oneidensis.
abstract: BACKGROUND
  Cytochrome bd oxidase, existing widely in bacteria, produces a proton motive force by the vectorial charge transfer of protons and more importantly, endows bacteria with a number of vitally important physiological functions, such as enhancing tolerance to various stresses. Although extensively studied as a CydA-CydB two-subunit complex for decades, the complex in certain groups of bacteria is recently found to in fact consist of an additional subunit, which is functionally essential.
  
  
  METHODS
  We investigated the assembly of the CydA-CydB complex using BiFC. We investigated the function of CydX using mutational analysis.
  
  
  RESULTS
  CydX, a 38-amino-acid inner-membrane protein, is associated with the CydA-CydB complex in Shewanella oneidensis, a facultative anaerobe renowned for its respiratory versatility. It is clear that CydX is neither required for the in vivo assembly of the CydA-CydB complex nor relies on the complex for its translocation and integration into the membrane. The N-terminal segment (1-25 amino acid residues) and short periplasmic overhang of CydX, with respect to functionality, are important whereas the remaining C-terminal segment is rather flexible.
  
  
  CONCLUSIONS
  Based on these findings, we postulate that CydX may function by positioning and stabilizing the prosthetic hemes, especially heme d in the CydA-CydB complex although a role of participating in catalytic reaction is not excluded.
  
  
  CONCLUSIONS
  The work provides novel insights into our understanding of the small subunit of the cytochrome bd oxidase.
authors.affiliation: Institute of Microbiology and College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, China.
authors.forename: Haijiang
authors.initials: H
authors.lastname: Chen
authors.affiliation: Institute of Microbiology and College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, China.
authors.forename: Qixia
authors.initials: Q
authors.lastname: Luo
authors.affiliation: Institute of Microbiology and College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, China.
authors.forename: Jianhua
authors.initials: J
authors.lastname: Yin
authors.affiliation: Institute of Microbiology and College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, China.
authors.forename: Tong
authors.initials: T
authors.lastname: Gao
authors.affiliation: Institute of Microbiology and College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, China. Electronic address: haichung@zju.edu.cn.
authors.forename: Haichun
authors.initials: H
authors.lastname: Gao
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003580:Cytochromes / Q000235:genetics / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000235:genetics / Q000378:metabolism*; D006418:Heme / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D020592:Shewanella / Q000201:enzymology* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D003580:Cytochromes; D008565:Membrane Proteins; D006418:Heme; D003576:Electron Transport Complex IV
keywords: CydX; Shewanella; bd oxidase