Understanding the molecular basis of Nitric oxide detoxification by M.tuberculosis Truncated Hemoglobin N.

MARCELO A MARTI

Pretoria South Africa

Workshop; Workshop on Advanced Design and Development of potential Drugs against Tuberculosis.; 2009

ICS-UNIDO

<!-- @page { size: 8.5in 11in; margin: 0.79in } P { margin-bottom: 0.08in } --> Mycobacterium tuberculosis, the causative agent of human tuberculosis, encodes a small haeme protein named Truncated Haemoglobin N (trHbN), which in its active site transforms nitric oxide (NO) to nitrate anion NO3-. The NO-dioxygenase activity of trHbN seems to be crucial for the bacillus, which can survive under the nitrosative stress conditions that occur upon infection of the host. As a defense mechanism against the copious amounts of NO produced by macrophages upon infection, the protein must achieve a high level of NO-dioxygenase activity to eliminate NO, activity which is modulated by its efficiency in capturing both susbtrates O2 and NO. To fulfill this task, migration of these small diatomic ligands through the protein matrix relies on the presence of a doubly branched tunnel system connecting the surface and the haem active site. Using state of the art computer simulation techniques we have studied the structural and dynamical factors that controls small ligand migration and affinity, NO oxidation reaction, and the product release steps. The results support a dual path mechanism for migration of O2 and NO through distinct branches of the tunnel, where migration of NO is allosterically facilitated upon binding of O2 to the haem group. The NO oxidation reaction occurs almost barrierless highlighting the importance of entry rate. Finally, egression of NO3 is preceded by the entrance of water to the haem cavity and occurs through a different pathway. Overall, the results highlight the intimate relationship between structure, dynamical behavior and biological function of trHbN.