Combining Mycobacterium tuberculosis proteome structural druggability and nitrosative stress sensitivity to determine potential latent phase specific targets

LUCAS DEFELIPE; DARÍO FERNÁNDEZ DO PORTO; PABLO IVAN RAMOS; MARISA NICOLAS; LEANDRO RADUSKY; ESTEBAN LANZAROTTI; ADRIAN TURJANSKI; MARCELO MARTI

Buenos Aires

Congreso; XI Congreso Argentino de Microbiología General; 2015

SAMIGE

The hosts immune response to tuberculosis (TB) infection relies in phagocytosis of the bacilli by macrophages that leads to the formation of granuloma which stops bacterial replication. Inside this structure bacteria face stressful conditions characterized by hypoxia, inducible Nitric Oxide (NO) synthase derived NO and nutrient deprivation, and in response switches to a non replicative state, known as dormancy phase (latency), where it can remain hidden and alive for decades. It is important to highlight that the existing anti­TB drugs are ineffective against dormant Mt, and that there is lack of well­defined targets specific for this state. With this in mind, we performed an in-silico detailed evaluation of Mt druggable proteome and we studied the relation with its sensitivity to nitrosative stress conditions and its relevance in the general metabolism of the bacteria to find putative terapheutics tagets of Mtb in latency. Many of the found targets are broadly mentioned in the literature such as signaling proteins(pnkB, pnkG, DevS), related to mycolic acid synthesis (IhnA, pcaA, pks13, fas, fad32D),panthenoate biosynthesis (panB) and Cytochromes (cyp 121 and cyp125). On the other hand, none of previous reports highlighted proteins in the mycothiol synthesis pathway (like mshB and ino1) as relevant drug targets. Ino1 is part of the DosR regulon. Its product; Inositol­3­phosphate synthase, I3PS; converts Glucose­6­P to 1D­myo­inositol 3­phosphate and had been previously reported as essential and highly overexpressed under starving conditions. I3PS strcutre presents a druggable pocket (DS score of 0.719) which overlaps with the NAD binding site, a site also known to be able to host drug like compounds in other proteins like InhA. Interestingly it displays 2 RNOS sensitive residues Tyr145 and Cys26 as well as a ?structural/catalytic Zn? whose role hasnot been completely elucidated. Clearly I3PS harbors all characteristics of an ideal target. Another interesing cases are both the lipoate synthesis pathway (lipA and lipB), responsible for the systhesis of this essential enzymatic cofactor and the L­D transpeptidase which is involved in the crosslinking of peptidoglycan in the mycobacterial cell wall (and thus related to the Mycolic acid biosynthesis) fundamental for in vivo resistance. LDTP1 is an enzyme involved in formation of peptidoglican cross­linking bonds, and thus essential. It is over­expressed under different stress conditions that mimic latency conditions. It is druggable (DS score of 0.701) and the active site pocket holds the key Cys226 which is the nucleophile in the enzymatic reaction, strongly arguing in favour of its potential inhibition by RNOS. Interestingly, it has also been suggested that LDTP1 catalytic activity could be inhibited by beta lactamic compounds.