Lauric acid and myristic acid from Allium sativum inhibit the growth of Mycobacterium tuberculosis H37Ra: in silico analysis reveals possible binding to protein kinase B.
BACKGROUND
The bulb of Allium sativum Linn (Alliaceae) has numerous medicinal values. Though the petroleum ether extract of the bulb has shown to exhibit antimycobacterial activity, the phytochemical(s) responsible for this inhibitory activity is not known.


OBJECTIVE
To characterize the bioactive compounds in the petroleum ether extract of Allium sativum (garlic) that inhibit the growth of Mycobacterium tuberculosis H37Ra.


METHODS
Bioactivity-guided fractionation was employed to isolate the bioactive compounds. Antimycobacterial activity was evaluated by well-diffusion method and microplate alamar blue assay (MABA). Infrared spectroscopy, mass spectrometry and nuclear magnetic resonance spectroscopy were used to characterize the bioactive compounds. Autodock was used to obtain information on molecular recognition, and molecular dynamics simulation was performed using GROMACS.


RESULTS
The bioactive compounds that inhibited the growth of M. tuberculosis H37Ra were found to be lauric acid (LA) and myristic acid (MA). The minimal inhibitory concentration of LA and MA was found to be 22.2 and 66.7 μg/mL, respectively. In silico analysis revealed that these fatty acids could bind at the cleft between the N-terminal and C-terminal lobes of the cytosolic domain of serine/threonine protein kinase B (PknB).


CONCLUSIONS
The inhibition activity was dependent on the alkyl chain length of the fatty acid, and the amino acid residues involved in binding to fatty acid was found to be conserved across the Pkn family of proteins. The study indicates the possibility of using fatty acid derivatives, involving Pkn family of proteins, to inhibit the signal transduction processes in M. tuberculosis.
a School of Bio Sciences and Technology, VIT University , Vellore , Tamil Nadu , India.
Rajiniraja
R
Muniyan
a School of Bio Sciences and Technology, VIT University , Vellore , Tamil Nadu , India.
Jayaraman
J
Gurunathan
D000995:Antitubercular Agents / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology; D003198:Computer Simulation; D005737:Garlic; D006801:Humans; D007850:Lauric Acids / Q000302:isolation & purification / Q000378:metabolism* / Q000494:pharmacology; D009169:Mycobacterium tuberculosis / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D019814:Myristic Acid / Q000302:isolation & purification / Q000378:metabolism* / Q000494:pharmacology; D010936:Plant Extracts / Q000302:isolation & purification / Q000378:metabolism* / Q000494:pharmacology; D018517:Plant Roots; D011485:Protein Binding / Q000502:physiology; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051057:Proto-Oncogene Proteins c-akt / Q000737:chemistry / Q000378:metabolism*
D000995:Antitubercular Agents; D007850:Lauric Acids; D010936:Plant Extracts; D019814:Myristic Acid; C030358:lauric acid; D051057:Proto-Oncogene Proteins c-akt
Bioactivity-guided fractionation; microplate Alamar blue assay; molecular dynamic simulations; petroleum ether extract; spectroscopic analysis