1NGK: Crystallographic Structure Of Mycobacterium Tuberculosis Hemoglobin O

Truncated hemoglobins (Hbs) are small hemoproteins, identified in microorganisms and in some plants, forming a separate cluster within the Hb superfamily. Two distantly related truncated Hbs, trHbN and trHbO, are expressed at different developmental stages in Mycobacterium tuberculosis. Sequence analysis shows that the two proteins share 18% amino acid identities and belong to different groups within the truncated Hb cluster. Although a specific defense role against nitrosative stress has been ascribed to trHbN (expressed during the Mycobacterium stationary phase), no clear functions have been recognized for trHbO, which is expressed throughout the Mycobacterium growth phase. The 2.1-A crystal structure of M. tuberculosis cyano-met trHbO shows that the protein assembles in a compact dodecamer. Six of the dodecamer subunits are characterized by a double conformation for their CD regions and, most notably, by a covalent bond linking the phenolic O atom of TyrB10 to the aromatic ring of TyrCD1, in the heme distal cavity. All 12 subunits display a cyanide ion bound to the heme Fe atom, stabilized by a tight hydrogen-bonded network based on the (globin very rare) TyrCD1 and TrpG8 residues. The small apolar AlaE7 residue leaves room for ligand access to the heme distal site through the conventional "E7 path," as proposed for myoglobin. Different from trHbN, where a 20-A protein matrix tunnel is held to sustain ligand diffusion to an otherwise inaccessible heme distal site, the topologically related region in trHbO hosts two protein matrix cavities.
PDB ID: 1NGKDownload
MMDB ID: 23020
PDB Deposition Date: 2002/12/17
Updated in MMDB: 2007/10
Experimental Method:
x-ray diffraction
Resolution: 2.11  Å
Source Organism:
Similar Structures:
Biological Unit for 1NGK: dodecameric; determined by author and by software (PISA)
Molecular Components in 1NGK
Label Count Molecule
Proteins (12 molecules)
Hemoglobin-like Protein HBO
Molecule annotation
Chemicals (42 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB