Dimethyl propionate ester heme-containing cytochrome b5: structure and stability

  • Lucia Banci
  • Ivano Bertini
  • Bruce R. Branchini
  • Parvana Hajieva
  • Georgios A. Spyroulias
  • Paola Turano
Original Article

DOI: 10.1007/s007750100217

Cite this article as:
Banci, L., Bertini, I., Branchini, B.R. et al. JBIC (2001) 6: 490. doi:10.1007/s007750100217

Abstract

A derivative of rat microsomal cytochrome b5, obtained by substitution of the native heme moiety with protoporphyrin IX dimethyl ester, has been characterized by 1H and 15N NMR spectroscopy. Besides the two usual A and B forms, which depend on the orientation of the heme in the prostethic group cavity, two other minor forms have been detected which presumably indicate different conformations of the vinyl side chains. The shifts of the heme methyls, as well as the directions of the rhombic axes of the magnetic susceptibility tensor, indicate a small difference in the orientation of the imidazole planes of the histidine axial ligands. The solution structure was determined by using 1303 meaningful NOEs and 241 pseudocontact shifts, the latter being derived from the native reduced protein. A family of 40 energy-minimized conformers was obtained with average RMSD of 0.56±0.09 Å and 1.04±0.12 Å for backbone and heavy atoms, respectively, and distance and pseudocontact shift penalty functions of 0.50±0.07 Å2 and 0.51±0.02 ppm2. The structure shows some changes around the cavity and in particular a movement of the 60–70 backbone segment owing to the absence of two hydrogen bonds between the Ser64 backbone NH and side-chain OH and the carboxylate oxygen of propionate-7, present in the native protein. The analysis of the NMR spectra in the presence of unfolding agents indicates that this protein is less stable than the native form. The decrease in stability may be the result of the loss of the two hydrogen bonds connecting propionate-7 to Ser64 in the native protein. The available data on the reduction potential and the electron transfer rates are discussed on the basis of the present structural data.

Keywords

Cytochrome b5 Stability Electron transfer protein Modified heme 

Abbreviations

DME

dimethyl ester of protohemin IX

GdmCl

guanidinium chloride

HMQC

heteronuclear multiple quantum coherence

HSQC

heteronuclear single quantum coherence

INEPT

insensitive nuclei enhanced by polarization transfer

NOE

nuclear Overhauser effect

NOESY

nuclear Overhauser effect spectroscopy

pcs

pseudocontact shift

REM

restrained energy minimization

RMSD

root mean-square deviation

TPPI

time-proportional phase incrementation

WATERGATE

water suppression by gradient-tailored excitation

Copyright information

© SBIC 2001

Authors and Affiliations

  • Lucia Banci
    • 1
  • Ivano Bertini
    • 1
  • Bruce R. Branchini
    • 2
  • Parvana Hajieva
    • 1
  • Georgios A. Spyroulias
    • 1
  • Paola Turano
    • 1
  1. 1.Magnetic Resonance CenterUniversity of FlorenceSesto FiorentinoItaly
  2. 2.Department of ChemistryConnecticut CollegeNew LondonUSA

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