Role of Pre-A motif in nitric oxide scavenging by truncated hemoglobin, HbN, of Mycobacterium tuberculosis.

Abstract

Mycobacterium tuberculosis truncated hemoglobin, HbN, is endowed with a potent nitric-oxide dioxygenase activity and has been found to relieve nitrosative stress and enhance in vivo survival of a heterologous host, Salmonella enterica Typhimurium, within the macrophages. These findings implicate involvement of HbN in the defense of M. tuberculosis against nitrosative stress. The protein carries a tunnel system composed of a short and a long tunnel branch that has been proposed to facilitate diatomic ligand migration to the heme and an unusual Pre-A motif at the N terminus, which does not contribute significantly to the structural integrity of the protein, as it protrudes out of the compact globin fold. Strikingly, deletion of Pre-A region from the M. tuberculosis HbN drastically reduces its ability to scavenge nitric oxide (NO), whereas its insertion at the N terminus of Pre-A lacking HbN of Mycobacterium smegmatis improved its nitric-oxide dioxygenase activity. Titration of the oxygenated adduct of HbN and its mutants with NO indicated that the stoichiometric oxidation of protein is severalfold slower when the Pre-A region is deleted in HbN. Molecular dynamics simulations show that the excision of Pre-A motif results in distinct changes in the protein dynamics, which cause the gate of the tunnel long branch to be trapped into a closed conformation, thus impeding migration of diatomic ligands toward the heme active site. The present study, thus, unequivocally demonstrates vital function of Pre-A region in NO scavenging and unravels its unique role by which HbN might attain its efficient NO-detoxification ability.

• Authors: Amrita Lama, Sudesh Pawaria, Axel Bidon-Chanal, Arvind Anand, José Luis Gelpí, Swati Arya, Marcelo Martí, Dario A Estrin, F Javier Luque, Kanak L Dikshit
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 284 Issue 21 Pg. 14457-68 (May 22 2009) ISSN: 0021-9258 [Print] United States
• PMID: 19329431 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Free Radical Scavengers
• Mutant Proteins
• Truncated Hemoglobins
• Nitric Oxide

Topics

• Amino Acid Motifs
• Amino Acid Sequence
• Circular Dichroism
• Computer Simulation
• Crystallography, X-Ray
• Escherichia coli (drug effects)
• Free Radical Scavengers (metabolism)
• Models, Molecular
• Molecular Sequence Data
• Mutant Proteins (chemistry, metabolism)
• Mycobacterium smegmatis (drug effects, metabolism)
• Mycobacterium tuberculosis (drug effects, metabolism)
• Nitric Oxide (metabolism, toxicity)
• Oxidation-Reduction (drug effects)
• Pliability (drug effects)
• Protein Structure, Secondary
• Sequence Deletion (drug effects)
• Structure-Activity Relationship
• Thermodynamics
• Truncated Hemoglobins (chemistry, metabolism)