title: The Mycobacterium tuberculosis Ag85A is a novel diacylglycerol acyltransferase involved in lipid body formation.
abstract: Mycobacterium tuberculosis accumulates large amounts of triacylglycerol (TAG) which acts as storage compounds for energy and carbon. The mycobacterial triacylglycerols stored in the form of intracellular lipid droplets are essential for long-term survival of M. tuberculosis during a dormant state. We report here that when the M. tuberculosis mycolytransferase Ag85A is overexpressed in Mycobacterium smegmatis mc(2)155, cell morphology was changed and the cells became grossly enlarged. A massive formation of lipid bodies and a change in lipid pattern was observed simultaneously. We suspected a possible role of Ag85A in the acyl lipid metabolism and discovered that the enzyme possesses acyl-CoA:diacylglycerol acyltransferase (DGAT) activity in addition to its well-known function as mycolyltransferase. Ag85A mediates the transesterification of diacylglycerol using long-chain acyl-CoA as acyl donors. The K(m) and K(cat) values for palmitoleoyl-coenzyme A were 390 µM and 55.54 min(-1) respectively. A docking model suggests that palmitoleoyl-coenzyme A and 1,2-dipalmitin occupy the same active site as trehalose 6,6'-dimycolate and trehalose 6'-monomycolate. The site-directed Ser126Ala mutation of the active site proved that this residue is involved in the catalytic activity of this enzyme. Although not proven conclusively for dormant stage of M. tuberculosis, our novel finding about the synthesis of TAGs by Ag85A strongly suggests that Ag85A may play a significant role in the formation of lipid storage bodies and thus also in the establishment and maintenance of a persistent tuberculosis infection.
authors.affiliation: Department of Gene Regulation and Differentiation, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany.
authors.forename: Ayssar A
authors.initials: AA
authors.lastname: Elamin
authors.forename: Matthias
authors.initials: M
authors.lastname: Stehr
authors.forename: Ralf
authors.initials: R
authors.lastname: Spallek
authors.forename: Manfred
authors.initials: M
authors.lastname: Rohde
authors.forename: Mahavir
authors.initials: M
authors.lastname: Singh
mesh_terms: D000217:Acyltransferases / Q000235:genetics / Q000378:metabolism*; D000942:Antigens, Bacterial / Q000235:genetics / Q000378:metabolism*; D020134:Catalytic Domain; D051048:Diacylglycerol O-Acyltransferase / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D007700:Kinetics; D050356:Lipid Metabolism; D053858:Metabolic Networks and Pathways; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D020102:Mycobacterium smegmatis / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D009169:Mycobacterium tuberculosis / Q000201:enzymology* / Q000378:metabolism*; D014280:Triglycerides
chemical_list: D000942:Antigens, Bacterial; D014280:Triglycerides; D000217:Acyltransferases; C112580:antigen 85A, Mycobacterium tuberculosis; D051048:Diacylglycerol O-Acyltransferase