The role of the supernumerary subunit of Rhodobacter sphaeroides cytochrome bc1 complex.

Journal Article (Journal Article;Review)

The smallest molecular weight subunit (subunit IV), which contains no redox prosthetic group, is the only supernumerary subunit in the four-subunit Rhodobacter sphaeroides bc1 complex. This subunit is involved in Q binding and the structural integrity of the complex. When the cytochrome bc1 complex is photoaffinity labeled with [3H]azido-Q derivative, radioactivity is found in subunits IV and I (cytochrome b), indicating that these two subunits are responsible for Q binding in the complex. When the subunit IV gene (fbcQ) is deleted from the R. sphaeroides chromosome, the resulting strain (RSdeltaIV) requires a period of adaptation before the start of photosynthetic growth. The cytochrome bc1 complex in adapted RSdeltaIV chromatophores is labile to detergent treatment (60-75% inactivation), and shows a four-fold increase in the Km for Q2H2. The first two changes indicate a structural role of subunit IV; the third change supports its Q-binding function. Tryptophan-79 is important for structural and Q-binding functions of subunit IV. Subunit IV is overexpressed in Escherichia coli as a GST fusion protein using the constructed expression vector, pGEX/IV. Purified recombinant subunit IV is functionally active as it can restore the bc1 complex activity from the three-subunit core complex to the same level as that of wild-type or complement complex. Three regions in the subunit IV sequence, residues 86-109, 77-85, and 41-55, are essential for interaction with the core complex because deleting one of these regions yields a subunit completely or partially unable to restore cytochrome bc1 from the core complex.

Full Text

Duke Authors

Cited Authors

  • Yu, L; Tso, SC; Shenoy, SK; Quinn, BN; Xia, D

Published Date

  • June 1999

Published In

Volume / Issue

  • 31 / 3

Start / End Page

  • 251 - 257

PubMed ID

  • 10591531

International Standard Serial Number (ISSN)

  • 0145-479X

Digital Object Identifier (DOI)

  • 10.1023/a:1005423913639


  • eng

Conference Location

  • United States