Bioinformatics Centre, Biochemistry & JBTDRC, MGIMS, Sevagram, Maharashtra, India
Received date: September 11, 2016; Accepted date: October 17, 2016; Published date: October 20, 2016
Citation: Jena L, Nayak T, Deshmukh S, Wankhade G, Waghmare P, et al. (2016) Isoniazid with Multiple Mode of Action on Various Mycobacterial Enzymes Resulting in Drug Resistance. J Infect Dis Ther 4:297. doi:10.4172/2332-0877.1000297
Copyright: © 2016 Jena L, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Isoniazid (INH), is one of the drugs shown to be effective and has been extensively used in TB control. Interestingly tuberculosis showed predominant drug resistance to isoniazid and thus lead to multi drug therapy in TB treatment. However, isoniazid is still advocated in latent TB and use as prophylactic in HIV infection and in children for prevention of TB. It is of interest that different studies revealing interaction of isoniazid with around 117 enzymes of mycobacteria influencing metabolic pathways by number of ways in addition to inhibiting mycolic acid synthesis and thus affecting growth of mycobacteria. The purpose of this review is to present the various mechanisms of action of isoniazid at different enzymes of MTB causing drug resistance.
Tuberculosis; Isoniazid; Drug resistance; Mycobacterium; Metabolic pathway
Tuberculosis (TB), being an oldest infectious disease, has been a major health problem worldwide. It is caused by Mycobacterium tuberculosis (MTB) which infects around one third of the world’s population. According to WHO Global Tuberculosis Report 2015, there were around 9.6 million people with active TB infection and amongst them 12% were HIV-positive. Further, in 2014 there were only 1,23,000 reported cases of multidrug-resistant TB (MDR-TB) amongst 4,80,000 cases [1]. The occurrences of extensively drug-resistant (XDR) tuberculosis have also been a rising risk in different regions around the globe [2]. The isoniazid (INH), also known as isonicotinyl hydrazine, one of the effective anti-TB drugs used for tuberculosis treatment is found to be resistant in different clinical strains of MTB [3]. Further, according to various studies, 82 different enzymes of mycobacteria associated with the interaction of INH, resulting in mutation and isoniazid drug resistance (Table 1) [4,5].
S/No | Locus tag | Name | Protein Length | Gene name |
PDB ID | Mutation | Pathway |
---|---|---|---|---|---|---|---|
1 | Rv1772 | hypothetical protein Rv1772 | 103 | - | - | Thr4Ala | |
2 | Rv1909c | ferric uptake regulation protein furA (furA) | 150 | furA | - | Ser5Pro | |
3 | Rv0340 | hypothetical protein Rv0340 | 179 | - | - | Val163Ile | |
4 | Rv2428 | alkyl hydroperoxide reductase subunit C | 195 | ahpC | 2BMX | Inter-genic region G(-46)A |
|
5 | Rv1483 | 3-oxoacyl-[acyl-carrier-protein] reductase | 247 | fabG1 | 1UZL | Ala5Pro, Val14Leu, Thr21Ala | Fatty acid biosynthesis |
6 | Rv1484 | enoyl-(acyl carrier protein) reductase | 269 | inhA | 1P44 | Lys8Asn, Ile16Thr, Ile21Val/Thr, Ile47Thr, Val78Ala, Ser94Ala/Leu, Ile95Pro, Ile95Thr, Ile194Thr, Arg202Gly, Glu217Asp, promoter region |
Fatty acid biosynthesis |
7 | Rv3566c | arylamine n-acetyltransferase nat | 283 | nat | 4BGF | Gly67Arg, Gly207Glu | • Nitrotoluene degradation • Metabolic pathways • Biosynthesis of secondary metabolites |
8 | Rv2243 | acyl-carrier-protein S-malonyltransferase | 302 | fabD | 2QC3 | Ser275Asn | • Fatty acid biosynthesis • Metabolic pathways • Fatty acid metabolism |
9 | Rv0129c | secreted antigen 85-C FBPC (85C) | 340 | fbpC | 4MQM | Gly158Ser -63(C/T), -23(A/C) |
Glycerolipid metabolism |
10 | Rv2242 | hypothetical protein Rv2242 | 414 | - | - | Asp3Gly, Met323Thr | |
11 | Rv2245 | 3-oxoacyl-(acyl carrier protein) synthase II | 416 | kasA | 4C6U | Asp66Asn, Met77Ile, Arg121Lys, Gly269Ser, Gly312Ser, Gly387Asp, Phe413Leu | Fatty acid biosynthesis |
12 | Rv1592c | hypothetical protein Rv1592c | 446 | - | - | Pro42Leu, Val430Ala | |
13 | Rv1854c | NADH dehydrogenase | 463 | ndh | - | Arg13Cys, Val18Ala, Thr110Ala, Leu239Pro, Arg268His | Oxidative phosphorylation |
14 | Rv3139 | acyl-CoA dehydrogenase FADE24 | 468 | fadE24 | - | Insertion of 2 base pair (bp) at nucleotide position -64 | |
15 | Rv2247 | acetyl/propionyl-CoA carboxylase beta subunit AccD6 | 473 | accD6 | 4FB8 | Asp229Gly | • Fatty acid biosynthesis • Valine, leucine and isoleucine degradation • Pyruvate Metabolism • Glyoxylate and dicarboxylate metabolism • Propanoate Metabolism • Carbon Metabolism • Fatty acid metabolism |
16 | Rv0341 | isoniazid inductible gene protein INIB | 479 | iniB | - | Deletion of 12 bp at nucleotide position 665 | |
17 | Rv0343 | isoniazid inductible gene protein INIC | 493 | iniC | - | Trp83Gly | |
18 | Rv2846c | integral membrane efflux protein EfpA | 530 | efpA | - | Ile73Thr | |
19 | Rv0342 | isoniazid inductible gene protein INIA | 640 | iniA | - | Pro3Ala, Arg537His | |
20 | Rv1908c | catalase-peroxidase-peroxynitritase T KatG | 740 | katG | 2CCA | Ser315Thr, Ser315Asn, Arg463Leu, Ser17Asn, Gly19Asp, Ser140Asn/Arg, Gly279Asp, Gly285Asp, Gly316Asp, Ser457Ile, Gly593Asp |
• Reactive oxygen species degradation • superoxide radicals degradation • Phenylalanine metabolism • Tryptophan metabolism • Metabolic Pathways • Biosynthesis of secondary metabolites |
21 | Rv3795 | integral membrane indolylacetylinositol arabinosyltransferase EMBB | 1098 | embB | - | Tyr333His | • Cell wall biosynthesis • Mycolyl-arabinogalactan-peptidoglycan complex biosynthesis |
22 | Rv2427a | Transcriptional regulator OxyR', pseudogene | oxyR' | - | - | ||
23 | Rv0236c | Alpha-(1>3)-arabino-furanosyltransferase | 1,400 | aftD | - | Thr797Ala | Cell wall polysaccharide biosynthesis |
24 | Rv0932c | Phosphate-binding protein | 370 | pstS2 | Arg70Leu | • ABC transporters, • Two-component system • Tuberculosis |
|
25 | Rv0985c | Large-conductance mechano sensitive channel | 151 | mscL | 2OAR | Gly55Ala | |
26 | Rv0987 | ABC transporter substrate-binding protein | 855 | - | Ala819Pro | ||
27 | Rv1877 | MFS-type transporter | 687 | Val660Phe | |||
28 | Rv2576c | membrane protein | 154 | - | Hia128Arg | ||
29 | Rv2999 | Peptidase M23B | 321 | lppY | Met313Thr | ||
30 | Rv3382c | 4-hydroxy-3-methylbut-2-enyl diphosphate reductase 2 | 329 | ispH2 | Gln178Arg | • Terpenoid backbone biosynthesis • Metabolic Pathways • Biosynthesis of secondary metabolites • Biosynthesis of antibiotics |
|
31 | Rv3448 | ESX-4 secretion system protein | 467 | eccD4 | - | Ala193Pro | |
32 | Rv0194 | Multidrug efflux ATP-binding/ permease protein | 1194 | Leu350Phe, Asp536His | |||
33 | Rv0338c | FeS-binding protein | 882 | Lys490Asn | |||
34 | Rv0517 | Possible membrane acyltransferase | 436 | Ser408Gly | |||
35 | Rv0793 | Putative monooxygenase | 101 | 1YOH | Gly81Asp | Antibiotic biosynthesis | |
36 | Rv0886 | Probable ferredoxin / ferredoxin-NADP reductase | 575 | fprB | Ile413Phe | • Metabolic Pathway • Photosynthesis |
|
37 | Rv1023 | Enolase | 429 | eno | Ala348Ser | • Glycolysis / Gluconeogenesis • Methane Metabolism • Metabolic Pathways • Biosynthesis of secondary metabolites • Microbial Metabolism in diverse environments • Biosynthesis of Antibiotics • Carbon metabolism, • Biosynthesis of amino acids • RNA degradation |
|
38 | Rv1355c | molybdopterin biosynthesis protein | 715 | moeY | Ile710Val | Molybdopterin biosynthesis | |
39 | Rv1555 | Fumarate reductase subunit D | 125 | frdD | Ile103Thr | • Citrate cycle (TCA cycle) • Oxidative phosphorylation • Pyruvate Metabolism, • Butanoate Metabolism, • Metabolic Pathways • Biosynthesis of secondary metabolites • Microbial metabolism in diverse environments • Biosynthesis of Antibiotics • Carbon Metabolism |
|
40 | Rv1850 | Urease subunit alpha | 577 | ureC | Asp336Gly | • Arginine biosynthesis • Purine Metabolism • Metabolic Pathways • Microbial metabolism in diverse environments |
|
41 | Rv2967c | Pyruvate carboxylase | 1127 | pca | Thr482Met | • Citrate cycle (TCA cycle) • Pyruvate metabolism • Metabolic pathway • Carbon metabolism • Biosynthesis of amino acid |
|
42 | Rv3401 | glycosyl hydrolase | 786 | Leu114Pro | Metabolic pathway | ||
43 | Rv3537 | 3-oxosteroid 1- dehydrogenase | 563 | kstD | Ala148pro | • Steroid Degradation • Metabolic pathway • Microbial metabolic in environments |
|
44 | Rv0574c | Probable polyglutamine synthesis accessory protein | 380 | - | Val16Ile | Capsule biosynthesis | |
45 | Rv1118c | Conserved hypothetical protein | 286 | Gly30Cys | |||
46 | Rv1504c | Conserved hypothetical protein | 199 | Glu73Gly | |||
47 | Rv1896c | S-adenosyl-L-methionine-dependent methyltransferase | 303 | Lys132Glu | Methylation | ||
48 | Rv1977 | Conserved hypothetical protein | 348 | Ser2Pro | |||
49 | Rv2184c | hypothetical protein | 379 | Pro294Leu | |||
50 | Rv2432c | hypothetical protein | 136 | - | Tyr117His | ||
51 | Rv2917 | Alanine / arginine-rich protein | 626 | Thr95Ala | Cell wall synthesis | ||
52 | Rv3181c | Antitoxin protein | 150 | vapB49 | Val39Gly | ||
53 | Rv0131c | acyl-CoA dehydrogenase | 447 | fadE1 | Ala35Val | • Fatty acid Degradation • Valine, leucine ,isoleusine degradation • Beta alanine metabolism • Metabolic Pathway • Biosynthesis of secondary metabolism • Biosynthesis of Antibiotic • Carbon metabolism • Fatty acid Metabolism • Propanoate Metabolism |
|
54 | Rv1527c | Polyketide synthase | 2,108 | pks5 | Gly2040Asp | • Lipid Biosynthesis • Polyketide biosynthesis |
|
55 | Rv1729c | S-adenosylmethionine-dependent methyltransferase | 312 | His238Arg | Lipid metabolism | ||
56 | Rv2383c | phenyloxazoline synthase | 1,414 | mbtB | His1251Pro | • Mycobactin biosynthesis • Siderophore biosynthesis |
|
57 | Rv2384 | bifunctional salicyl-AMP ligase/salicyl-S-ArCP synthetase | 565 | mbtA | Gly18Ser | • Polyketide biosynthesis • Mycobactin biosynthesis • Siderophore biosynthesis |
|
58 | Rv3392c | Cyclopropane mycolic acid synthase 1 | 287 | cmaA1 | 1KP9 | Gln99Glu | Mycolic acid biosynthesis |
59 | Rv3480c | diacyglycerol O-acyltransferase | 497 | Glu315Ala | Triacylglycerol biosynthesis | ||
60 | Rv3649 | DEAD / DEAH box helicase domain containing protein | 771 | Asp459Gly | Information pathway | ||
61 | Rv0355c | PPE family protein | 3.300 | PPE8 | Leu1213Pro | lipid metabolism. | |
62 | Rv2659c | Prophage integrase | 375 | Val235Ala | |||
63 | Rv1198 | ESAT-6-like protein | 94 | esxL | 4GZR | Gln20Leu | |
64 | Rv1362c | Mce-associated membrane Protein | 220 | - | Asp95Ala | ||
65 | Rv2869c | Zinc metalloprotease | 404 | Rip1 | Lys95Thr | ||
66 | Rv2911 | D-alanyl-D-alanine carboxy Peptidase | 291 | dacB2 | 4RYE | Leu220Gln | Peptidoglycan biosynthetic |
67 | Rv0086 | Hydrogenase | 488 | hycQ | Ala322Val | Metabolism and respiration | |
68 | Rv1844c | 6-phosphogluconate dehydrogenase | 485 | gnd1 | Ala400Thr | • Pentose phosphate pathway • Glutathione Metabolism • Metabolic Pathways • Biosynthesis of secondary metabolites • Microbial metabolism in diverse environments • Biosynthesis of antibiotics • Carbon metabolism |
|
69 | Rv2296 | Haloalkane dehalogenase 1 | 300 | dhmA1 | Ala211Val | • Chlorocyclohexane and chlorobenzene degradation • Chloroalkane and chloroalkene degradation • Metabolic pathways • Microbial metabolism in diverse environments |
|
70 | Rv3299c | Probable arylsulfatase | 970 | AtsB | Arg439Trp | Sphingolipid metabolism | |
71 | Rv0104 | Hypothetical protein | 504 | Ile13Leu | Metabolic pathway | ||
72 | Rv1069c | Conserved hypothetical protein | 587 | - | Val465Met | ||
73 | Rv2955c | Hypothetical protein | 321 | - | Phe315Ile | ||
74 | Rv0564c | Glycerol-3-phosphate dehydrogenase 2 [NAD(P)+] | 341 | gpdA1 /gpsA | Pro131Ser | • Glycerophospholipid metabolism • Biosynthesis of secondary metabolites • CDP-diacylglycerol biosynthesis I • CDP- diacylglycerol biosynthesis II |
|
75 | Rv0726c | S-adenosyl-L-methionine- dependent methyltransferase |
367 | Leu258Pro | Lipid metabolism | ||
76 | Rv0667 | DNA-directed RNA polymerase subunit beta | 1,178 | rpoB | Asp435Val | • Information Pathways • Purine Metabolism • Pyrimidine Metabolism • Metabolic pathway • RNA polymerase |
|
77 | Rv1189 | ECF RNA polymerase sigma factor | 290 | sigI | Arg76Cys | Information pathway | |
78 | Rv0578c | PE-PGRS family protein | 1,306 | PE_PGRS7 | Ala785Thr | lipid metabolism | |
79 | Rv1753c | PPE family protein | 1,053 | ppe24 | Thr669Ser | lipid metabolism | |
80 | Rv0094c | Conserved hypothetical protein | 317 | Lys315Glu | |||
81 | Rv1358 | transcriptional regulatory protein | 1159 | TAG*1160Ser | Cyclic nucleotide biosynthesis |
||
82 | Rv0175 | Mce associated membrane protein | 213 | - | Met138Thr |
Table 1: Mutations in MTB Genes / Proteins reported to be associated with Isoniazid resistance [4,5].
As INH has been used as a first-line drug in the prevention and treatment of TB [6], its mechanism of action has been studied for more than five decades. It is reported to produce various highly reactive compounds [7] which then target multiple enzymes of MTB [8]. Thus, the complex mode of action of isoniazid with number of enzymes needs study. Further, it is useful to understand how mutation in different MTB enzymes affects drug-enzyme interaction. This communication reviews the various mechanism of action of a single drug isoniazid at different MTB enzymes leading to drug resistance.
Activation of INH by KatG and formation of INH-NAD(P) adduct
KatG of MTB encoded by Rv1908c has 740 amino acids in its protein sequence, is a multifunctional enzyme, showing both a catalase and a peroxynitritase activities [9,10]. Besides playing an important role in the intracellular survival of the pathogen within macrophages, it protects against reactive nitrogen and oxygen species produced by phagocytic cells [10]. Being a pro-drug, INH is activated by the catalase– peroxidase KatG and MnCl2 and forms isonicotinoyl radical or anion which then reacts with NAD+ and NADP+ [11], and subsequently generates INH-NAD(P) adducts [12]. Amongst these adducts, the INH-NAD reported to inhibit the enoyl-ACP reductase enzyme (InhA) whereas INH-NADP inhibit dfrA - encoded dihydrofolate reductase [13] and MabA (3-oxoacyl-ACP reductase) [14].
Inhibition of InhA by INH-NAD adduct
INH-NAD adduct was reported to inhibit InhA of MTB encoded by Rv1484 which is reported to block the synthesis of mycolic acid, a major lipid of the mycobacterial cell wall.
Our in silico docking study between InhA and truncated INH-NAD adduct, demonstrated that the adduct binds with InhA by forming a hydrogen bond with its substrate binding residue Tyr158 [15] which correlates the in vitro study by Nguyen et al. reporting that the INHNAD adduct as a potential inhibitor of InhA [16].
Truncated INH-NAD adduct
After profiling the MTB proteome using both the INH-NAD and INH-NADP adducts coupled to Sepharose solid supports, Argyrou et al. identified seventeen proteins (Table 2) that bind to these adducts with high affinity [13]. Further, the truncated form of INH–NAD adduct (4-isonicotinoylnicotinamide, 4-INN,) reported to have potential antimycobacterial activity [17]. The in silico docking study of truncated INH–NAD adducts with six MTB enzymes with known three-dimensional (3D) structure out of 17 proteins (Table 2), showed considerable binding affinity and thus revealing the truncated INH– NAD adducts as effective inhibitors for these proteins [15].
S/No | Locus_tag | Name | Protein Length |
Locus | PDB ID | Pathway |
---|---|---|---|---|---|---|
1 | Rv3248c | S-adenosyl-L-homocysteine hydrolase | 495 | sahH | 3DHY | • Cysteine and methionine • Metabolism • Metabolic pathways |
2 | Rv0753c | Methylmalonate-semialdehyde dehydrogenase |
510 | mmsA | • Valine, leucine and isoleucine • Degradation • beta-Alanine metabolism. • Inositol phosphate metabolism • Propanoate metabolism • Metabolic pathways • Carbon metabolism |
|
3 | Rv1187 | pyrroline-5-carboxylate dehydrogenase ROCA | 543 | rocA | 4IHI | • Alanine, aspartate and glutamate Metabolism • Arginine and proline metabolism • Metabolic pathways |
4 | Rv0155 | NAD(P) transhydrogenase subunit alpha |
366 | pntAa/ pntAA | • Nicotinate and nicotinamide metabolism • Metabolic pathways |
|
5 | Rv2623 | Universal stress protein | 297 | TB31.7 | 3CIS | |
6 | Rv1996 | hypothetical protein | 317 | |||
7 | Rv0468 | 3-hydroxybutyryl-CoA dehydrogenase | 286 | fadB2 | • Phenylalanine metabolism • Benzoate degradation • Butanoate metabolism • Metabolic pathways • Microbial metabolism in diverse environments |
|
8 | Rv1484 | enoyl-ACP reductase | 269 | inhA | 1P44 | • Fatty acid biosynthesis • Metabolic pathways |
9 | Rv2691 | TRK system potassium uptake protein CEOB |
227 | ceoB / trkA | ||
10 | Rv0091 | bifunctional 5-methylthioadenosine nucleosidase / S-adenosylhomocysteine nucleosidase | 255 | Mtn / pfs | • Cysteine and methionine metabolism • Metabolic pathways • Biosynthesis of amino acids, |
|
11 | Rv2858c | Aldehyde dehydrogenase | 455 | aldC | • Glycolysis / Gluconeogenesis • Pentose and glucuronate interconversions • Ascorbate and aldarate metabolism • Fatty acid degradation • Valine, leucine and isoleucine degradation • Lysine degradation • Arginine and proline metabolism • Histidine metabolism • Tryptophan metabolism • beta-Alanine metabolism • Glycerolipid metabolism • Pyruvate metabolism • Chloroalkane and chloroalkene degradation • Limonene and pinene degradation • Metabolic pathways • Biosynthesis of secondary metabolites • Microbial metabolism in diverse environments • Biosynthesis of antibiotics |
|
12 | Rv1059 | Hypothetical protein | 354 | |||
13 | Rv3777 | Oxidoreductase | 328 | |||
14 | Rv2971 | Oxidoreductase | 4OTK | |||
15 | Rv2766c | 3-ketoacyl-ACP reductase | 260 | |||
16 | Rv2671 | Possible bifunctional enzyme riboflavin biosynthesis protein RibD | 258 | ribD | • Riboflavin metabolism • Metabolic pathways • Biosynthesis of secondary metabolites |
|
17 | Rv2763c | Dihydrofolate reductase (DHFR) | 159 | dfrA/ folA | 4KL9 | • One carbon pool by folate • Folate biosynthesis • Metabolic pathways |
18 | Rv1483 | 3-oxoacyl-ACP reductase | 247 | fabG1 / mabA |
1UZL | • Fatty acid biosynthesis • Biotin metabolism • Biosynthesis of unsaturated fatty acids • Metabolic pathways |
Table 2: High Affinity INH-NAD (P) - binding proteins from Mycobacterium tuberculosis [13,14].
The arylamine N-acetyltransferase (NAT) of MTB also reported to have direct interaction with INH like KatG. As a drug-metabolizing enzyme, NAT acetylates INH and forms INH to a therapeutically inactive form i.e. N-acetylate INH [18]. Payton et al. observed that the over expression of NAT leads to increased INH resistance in Mycobacterium smegmatis [19]. Further, when the gene was knockedout, the bacteria showed increased sensitivity to INH [19].
Mutation in different mycobacterial enzymes associated with INH resistance
The mechanism of INH resistance has been the focus of extensive study. It is broadly reported that INH resistance in MTB has been associated with mutations in different genes [7] such as katG, inhA, kasA, ahpC etc. Mutation in NADH dehydrogenase, encoded by ndh also reported to be linked with INH resistance [20]. Further, mutation in promoter region of inhA strongly linked with extensively drugresistant tuberculosis [21].
Besides 22 genes of MTB reported in Tuberculosis Drug Resistance Mutation Database, which were associated with INH resistance [4], Shekar et al. identified 60 novel genes associated with INH resistance in INH-resistant clinical isolates of MTB by their whole genome sequencing [5]. Most of the genes are associated with important metabolic pathways of MTB such as biosynthesis of secondary metabolites, antibiotics, amino acid, fatty acid; carbon metabolism; cell wall biosynthesis; glycolysis/gluconeogenesis, glutathione metabolism, glyoxylate and dicarboxylate metabolism, lipid biosynthesis, lipid metabolism, metabolic pathway, microbial metabolism in diverse environments, mycolic acid, nitrotoluene degradation, oxidative phosphorylation etc [22,23].
As KatG is associated with activation of INH, mutation in its gene plays an important role in INH resistance. Among various mutations identified in KatG, mutation at S315T and S315N has been widely reported in INH resistance strains. Our computational studies also showed that KatG mutations (S315T/S315N) prevent free radical formation that leads to drug resistance [24].
Two mutations in NAT enzymes (G207E and G67R), reported in MTB clinical isolates associated with INH resistance. From the molecular dynamics (MD) simulation analysis of NAT wild type and mutants (G67R and G207E) models, it was observed that these mutations increases the stability of the binding interfaces of enzyme by providing extra electrostatic interaction with neighboring amino acids. This stability might facilitate in rapid acetylation of INH and detoxification and leads to isoniazid resistance [25].
The mycobacterial NADH pyrophosphatase (NudC) reported to have an important role in the degradation of INH-NAD adduct (the active forms of isoniazid) and ETH-NAD adduct (active form of ethionamide (ETH)) that leads to INH and ETH inactivation. The polymorphism P237Q leads to loss of enzymatic activity and thus leads to INH and ETH resistance [26,27]. Further, a silent mutation in mabA (Rv1483), at nucleotide position 609 (g609a), leads to INH resistance in MTB [28].
Mycothiol (MSH), a major low molecular mass thiol in mycobacteria has antioxidant activity as well as the ability to detoxify a variety of toxic compounds. Four genes such as mshA (Rv0486), mshB (Rv1170), mshC (Rv2130c) and mshD (Rv0819) involves in Mycothiol biosynthesis. Buchmeier et al. observed that the MTB mutant (613 bp deletion within the mshB gene) showing increase resistance to Isoniazid [29]. Further, the mshA (Rv0486) gene of MTB encoding glycosyltransferase involved in the first step of mycothiol biosynthesis [10]. Jagielski et al. observed that a defective mshA gene (frame shift mutation - insC1283) might contribute to the increase in isoniazid resistance [30].
The MTB glf (Rv3809c) gene encoding UDP-galactopyranose mutase, catalyzes the conversion of UDP-galactopyranose into UDPgalactofuranose through a 2-keto intermediate. It was reported that the over expression of Glf enzyme bound with the modified form of INH or by sequestering a factor such as NAD+ required for INH activity and thus might contribute to INH resistance [31]. Further, Pasca et al. observed that over expression of transmembrane transport protein MmpL7 encoded by mmpL7 (Rv2942) gene, in Mycobacterium smegmatis leads to high level INH resistance [32]. Yang et al. observed that InbR, a transcriptional regulatory protein which is encoded by Rv0275c, directly bind with INH and involved in isoniazid resistance [33]. Pandey et al. observed the over expression of Rv1475c (acn) gene, encoding Aconitate hydratase-A enzyme in clinical isolate of MTB resistant to rifampicin, isoniazid, ethambutol and kanamcyin [34] which suggested that Rv1475c might have some important role in INH resistance [35].
Though INH resistance is mostly due to the chromosomal mutations in the target genes, around 20-30% of INH resistant MTB isolates do not have mutations in any of the genes linked with resistance to INH [36] which suggests that other mechanism(s), namely efflux pump systems of MTB may be involved in INH resistance. The over expression of efflux pump genes such as efpA, mmpL7, mmr, p55 and the Tap-like gene Rv1258c etc are shown to contribute for INH resistance [36]. Further, efpA, jefA (Rv2459), drrA, drrB, mmr, Rv1250, Rv1634 and Rv0849 were reported to be over expressed under isoniazid or rifampicin stress [37]. Besides some other genes of MTB (Table 3) of an INH-sensitive strain, are also observed to be induced by isoniazid or ethionamide treatment [38].
S/No | Locus_tag | Name | Protein Length |
Locus | PDB ID | Pathway |
---|---|---|---|---|---|---|
1 | Rv2243 | Malonyl CoA-acyl carrier protein transacylase | 302 | FabD | 2QC3 | • Fatty acid biosynthesis • Lipid metabolism |
2 | Rv2244 | Meromycolate extension acyl carrier protein | 115 | acpM | 1KLP | |
3 | Rv2245 | 3-oxoacyl-[acyl-carrier-protein] synthase 1 | 416 | kasA | 4C6U | • Fatty acid biosynthesis • Lipid metabolism |
4 | Rv2246 | 3-oxoacyl-[acyl-carrier-protein] synthase 2 | 417 | kasB | fatty acid biosynthesis Lipid metabolism |
|
5 | Rv2247 | Propionyl-CoA carboxylase beta chain 6 | 473 | AccD6 | 4FB8 | • Fatty acid biosynthesis • Valine, leucine and isoleucine degradation • Pyruvate metabolism • Glyoxylate and dicarboxylate metabolism • Propanoate metabolism • Metabolic pathways • Biosynthesis of secondary metabolites • Microbial metabolism in diverse environments • Biosynthesis of antibiotics • Carbon metabolism • Fatty acid metabolism |
6 | Rv0129c | Diacylglycerol acyltransferase/mycolyl-transferase Ag85C | 340 | fbpC | 4MQM | • Glycerolipid metabolism • Metabolic pathways |
7 | Rv3140 | Acyl-CoA dehydrogenase | 401 | FadE23 | • Fatty acid degradation • Valine, leucine and isoleucine degradation • Beta-Alanine metabolism • Propanoate metabolism • Metabolic pathways • Biosynthesis of secondary metabolites • Biosynthesis of antibiotics • Carbon metabolism • Fatty acid metabolism |
|
8 | Rv3139 | Butyryl-CoA dehydrogenase | 468 | FadE24 | ||
9 | Rv2428 | Alkyl hydroperoxide reductase subunit C | 195 | ahpc | 2BMX | • Glutathione metabolism • Metabolic pathways |
10 | Rv2846c | MFS-type transporter EfpA | 530 | efpA | ||
11 | Rv1592c | Probable inactive lipase | 446 | |||
12 | Rv1772 | Hypothetical protein | 103 | |||
13 | Rv0341 | Isoniazid-induced protein | 479 | iniB | ||
14 | Rv0342 | Isoniazid-induced protein | 640 | iniA | ||
15 | Rv0343 | Isoniazid-induced protein | 493 | iniC |
Table 3: Genes induces by INH or ethionamide treatment of an INH-sensitive strain [38].
Though, the in depth molecular mechanism of INH resistance in number of mycobacterial proteins from drug resistance strains is yet to be thoroughly understood, many studies proposed the association of INH with number of MTB proteins in different ways such as direct activation by KatG, acetylation by NAT, inhibiting different enzymes through adduct formation, inducing different enzymes etc. Further, mutations in many enzymes of MTB are reported to be associated with INH resistances which are supposed to associate with different important metabolic pathways of MTB. The consequence of mutation of those enzymes on respective pathways needs further study so as to reveal other mechanisms of INH resistance.
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