PDBsum entry: 1i87

Electron transport

PDB id: 1i87

Contents

Protein chain

94 a.a. *

* Residue conservation analysis

PDB id:

1i87

Name:

Electron transport

Title:

Solution structure of the water-soluble fragment of rat hepatic apocytochrome b5

Structure:

Cytochrome b5. Chain: a. Fragment: water-soluble domain (residues 1-98). Synonym: apocytochrome b5. Engineered: yes

Source:

Rattus norvegicus. Norway rat. Organism_taxid: 10116. Expressed in: escherichia coli bl21(de3). Expression_system_taxid: 469008.

NMR struc:

20 models

Authors:

C.J.Falzone,Y.Wang,B.C.Vu,N.L.Scott,S.Bhattacharya, J.T.Lecomte

Key ref:

C.J.Falzone et al. (2001). Structural and dynamic perturbations induced by heme binding in cytochrome b5. Biochemistry, 40, 4879-4891. PubMed id: 11294656 DOI: 10.1021/bi002681g

Date:

12-Mar-01 Release date: 16-May-01

Protein chain

P00173  (CYB5_RAT) -  Cytochrome b5

Seq: 134 a.a.

Struc: 94 a.a.

 Gene Ontology (GO) functional annotation 

• Biochemical function: heme binding (1 term)

DOI no: 10.1021/bi002681g

Biochemistry 40:4879-4891 (2001)

PubMed id: 11294656

Structural and dynamic perturbations induced by heme binding in cytochrome b5.

C.J.Falzone, Y.Wang, B.C.Vu, N.L.Scott, S.Bhattacharya, J.T.Lecomte.

ABSTRACT

The water-soluble domain of rat hepatic cytochrome b(5) undergoes marked structural changes upon heme removal. The solution structure of apocytochrome b(5) shows that the protein is partially folded in the absence of the heme group, exhibiting a stable module and a disordered heme-binding loop. The quality of the apoprotein structure in solution was improved with the use of heteronuclear NMR data. Backbone amide hydrogen exchange was studied to characterize cooperative units in the protein. It was found that this criterion distinguished the folded module from the heme-binding loop in the apoprotein, in contrast to the holoprotein. The osmolyte trimethylamine N-oxide (TMAO) did not affect the structure of the apoprotein in the disordered region. TMAO imparted a small stabilization consistent with an unfolded state effect correlating with the extent of buried surface area in the folded region of the native apoprotein. The failure of the osmolyte to cause large conformational shifts in the disordered loop supported the view that the specificity of the local sequence for the holoprotein fold was best developed with the stabilization of the native state through heme binding. To dissect the role of the heme prosthetic group in forcing the disordered region into the holoprotein conformation, the axial histidine belonging to the flexible loop (His63) was replaced with an alanine, and the structural properties of the protein with carbon-monoxide-ligated reduced iron were studied. The His63Ala substitution resulted in a protein with lower heme affinity but nevertheless capable of complete refolding. This indicated that the coordination bond was not necessary to establish the structural features of the holoprotein. In addition, the weak binding of the heme in this protein resulted in conformational shifts at a location distant from the binding site. The data suggested an uneven distribution of cooperative elements in the structure of the cytochrome.