Structural highlights
Function
[TRHBN_MYCTU] Binds oxygen cooperatively with very high affinity (P(50) = 0.013 mmHg at 20 degrees Celsius) because of a fast combination (25 microM(-1).s(-1)) and a slow dissociation (0.2 s(-1)) rate.
Publication Abstract from PubMed
A unique defense mechanisms by which Mycobacterium tuberculosis protects itself from nitrosative stress is based on the O2 -dependent NO-dioxygenase (NOD) activity of truncated hemoglobin 2/2HbN (Mt2/2HbN). The NOD activity largely depends on the efficiency of ligand migration to the heme cavity through a two-tunnel (long and short) system; recently, it was also correlated with the presence at the Mt2/2HbN N-terminus of a short pre-A region, not conserved in most 2/2HbNs, whose deletion results in a drastic reduction of NO scavenging. In the present study, we report the crystal structure of Mt2/2HbN-DeltapreA, lacking the pre-A region, at a resolution of 1.53 A. We show that removal of the pre-A region results in long range effects on the protein C-terminus, promoting the assembly of a stable dimer, both in the crystals and in solution. In the Mt2/2HbN-DeltapreA dimer, access of heme ligands to the short tunnel is hindered. Molecular dynamics simulations show that the long tunnel branch is the only accessible pathway for O2 -ligand migration to/from the heme, and that the gating residue Phe(62)E15 partly restricts the diameter of the tunnel. Accordingly, kinetic measurements indicate that the kon value for peroxynitrite isomerization by Mt2/2HbN-DeltapreA-Fe(III) is four-fold lower relative to the full-length protein, and that NO scavenging by Mt2/2HbN-DeltapreA-Fe(II)-O2 is reduced by 35-fold. Therefore, we speculate that Mt2/2HbN evolved to host the pre-A region as a mechanism for preventing dimerization, thus reinforcing the survival of the microorganism against the reactive nitrosative stress in macrophages. DATABASE: Coordinates and structure factors have been deposited in the Protein Data Bank under accession number 5AB8.
The N-terminal pre-A region of Mycobacterium tuberculosis 2/2HbN promotes NO-dioxygenase activity.,Pesce A, Bustamante JP, Bidon-Chanal A, Boechi L, Estrin DA, Luque FJ, Sebilo A, Guertin M, Bolognesi M, Ascenzi P, Nardini M FEBS J. 2016 Jan;283(2):305-22. doi: 10.1111/febs.13571. Epub 2015 Nov 16. PMID:26499089[1]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Pesce A, Bustamante JP, Bidon-Chanal A, Boechi L, Estrin DA, Luque FJ, Sebilo A, Guertin M, Bolognesi M, Ascenzi P, Nardini M. The N-terminal pre-A region of Mycobacterium tuberculosis 2/2HbN promotes NO-dioxygenase activity. FEBS J. 2016 Jan;283(2):305-22. doi: 10.1111/febs.13571. Epub 2015 Nov 16. PMID:26499089 doi:http://dx.doi.org/10.1111/febs.13571
