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 language | English (US) |
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Pages (from-to) | 1021-1031 |
Number of pages | 11 |
Journal | Proteins: Structure, Function and Genetics |
Volume | 65 |
Issue number | 4 |
DOIs | |
State | Published - 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