Crystal structures of E. coli CcmG and its mutants reveal key roles of the N-terminal β-sheet and the fingerprint region

Nan Ouyang, Yong Guang Gao, Hong Yu Hu, Zong Xiang Xia

Research output: Contribution to journalArticlepeer-review

22 Scopus citations

Abstract

CcmG, also designated DsbE, functions as a periplasmic protein thiol:disulfide oxidoreductase and is required for cytochrome c maturation. Here we report the crystal structures of Escherichia coli CcmG and its two mutants, P144A and the N-terminal fifty seven-residue deletion mutant, and two additional deletion mutants were studied by circular dichroism. Structural comparison of E. coli CcmG with its deletion mutants reveals that the N-terminal β-sheet is essential for maintaining the folding topology and consequently maintaining the active-site structure of CcmG. Pro144 and Glu145 are key residues of the fingerprint region of CcmG. Pro144 is in cis-configuration, and it makes van der Waals interactions with the active-site disulfide Cys80-Cys83 and forms a C-H⋯O hydrogen bond with Thr82, helping stabilize the active-site structure. Glu145 forms a salt-bridge and hydrogen-bond network with other residues of the fingerprint region and with Arg158, further stabilizing the active-site structure. The cis-configuration of Pro144 makes the backbone nitrogen and oxygen of Ala143 exposed to solvent, favorable for interacting with binding partners. The key role of cis-Pro144 is verified by the P144A mutant, which contains trans-Ala144 and displays redox property changes. Structural comparison of E. coli CcmG with the recently reported structure of CcmG in complex with the N-terminal domain of DsbD reveals that Tyr141 undergoes conformational changes upon binding DsbD. A cis-proline located at the N-terminus of the first β-strand of the ββα motif of the thioredoxin-like domain is a conserved structural feature of the thioredoxin superfamily.

Original languageEnglish (US)
Pages (from-to)1021-1031
Number of pages11
JournalProteins: Structure, Function and Genetics
Volume65
Issue number4
DOIs
StatePublished - Dec 1 2006

Keywords

  • Circular dichroism
  • Cis-proline
  • Conformational change
  • Crystal structure
  • E. coli cytochrome c maturation protein
  • Fingerprint region
  • Mutant
  • N-terminal β-sheet
  • Redox potential
  • Thiol: disulfide oxidoreductase

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