Axial coordination of heme in ferric CcmE chaperone characterized by EPR spectroscopy.

Garcia Rubio, Ines ; Braun, M. ; Gromov, I. ; Thony-Meyer, L. ; Schweiger, Arthur

Resumen: In Escherichia coli cytochrome c maturation requires a set of eight proteins including the heme chaperone CcmE, which binds heme transiently, yet covalently. Several variants of CcmE were purified and analyzed by continuous-wave electron paramagnetic resonance, electron nuclear double resonance, and hyperfine sublevel correlation spectroscopy to investigate the heme axial coordination. Results reveal the presence of a number of coordination environments, two high-spin heme centers with different rhombicities, and at least one low-spin heme center. The low-spin species was shown to be an artifact induced by the presence of available histidines in the vicinity of the iron. Both of the high-spin forms are five-coordinated, and comparison of the spectra of the wild-type CcmE with those of the mutant CcmEY134H proves that the higher-rhombicity form is coordinated by Tyr134. The low-rhombicity (axial) form does not have a histidine residue or a water molecule as an axial ligand. However, we identified exchangeable protons coupled to the iron ion. We propose that the axial form can be coordinated by a carboxyl group of an acidic residue in the flexible domain of the protein. The two species would represent two different conformations of the flexible α-helix domain surrounding the heme. This conformational flexibility confers CcmE special dynamic properties that are certainly important for its function.

Idioma: Inglés

DOI: 10.1529/biophysj.106.098277

Año: 2007

Publicado en: BIOPHYSICAL JOURNAL 92, 4 (2007), 1361-1373
ISSN: 0006-3495

Factor impacto JCR: 4.627 (2007)

Categ. JCR: BIOPHYSICS rank: 10 / 67 = 0.149 (2007) - Q1 - T1

Tipo y forma: Article (Published version)