Abstract
The intracellular pathogen Mycobacterium tuberculosis is the causative agent of tuberculosis, which is a leading cause of mortality worldwide. The survival of M.tuberculosis in host macrophages through long-lasting periods of persistence depends, in part, on breaking down host cell lipids as a carbon source. The critical role of fatty-acid catabolism in this organism is underscored by the extensive redundancy of the genes implicated in β-oxidation (∼100 genes). In a previous study, the enzymology of the M. tuberculosis L-3-hydroxyacyl-CoA dehydrogenase FadB2 was characterized. Here, the crystal structure of this enzyme in a ligand-free form is reported at 2.1 Å resolution. FadB2 crystallized as a dimer with three unique dimer copies per asymmetric unit. The structure of the monomer reveals a dual Rossmann-fold motif in the N-terminal domain, while the helical C-terminal domain mediates dimer formation. Comparison with the CoA- and NAD+-bound human orthologue mitochondrial hydroxyacyl-CoA dehydrogenase shows extensive conservation of the residues that mediate substrate and cofactor binding. Superposition with the multi-catalytic homologue M. tuberculosis FadB, which forms a trifunctional complex with the thiolase FadA, indicates that FadB has developed structural features that prevent its self-association as a dimer. Conversely, FadB2 is unable to substitute for FadB in the tetrameric FadA-FadB complex as it lacks the N-terminal hydratase domain of FadB. Instead, FadB2 may functionally (or physically) associate with the enoyl-CoA hydratase EchA8 and the thiolases FadA2, FadA3, FadA4 or FadA6 as suggested by interrogation of the STRING protein-network database.
Highlights
The bacterial pathogen Mycobacterium tuberculosis (Mtb) is the ninth leading cause of mortality worldwide and remains the foremost cause of death caused by a single infectious agent (World Health Organization, 2018)
Recent evidence shows that Mtb degrades host cell cholesterol during persistence (Pandey & Sassetti, 2008; Wipperman et al, 2014) and that the inhibition of cholesterol degradation could provide a potential route to control the growth of Mtb in macrophages (VanderVen et al, 2015)
We characterized the enzymology of Mtb FadB2 (Rv0468) and showed that this enzyme catalyses the oxidation of 3-hydroxyacyl-coenzyme A (CoA) to acetoacetyl-CoA (Taylor et al, 2010)
Summary
The bacterial pathogen Mycobacterium tuberculosis (Mtb) is the ninth leading cause of mortality worldwide and remains the foremost cause of death caused by a single infectious agent (World Health Organization, 2018). Mtb evades immune clearance and enters a longlasting latency or persistence state. An obvious drawback of this survival strategy is that the organism must cope with an environment in which nutrient supply is scarce and, as a key adaptation, Mtb utilizes host cell lipids as a carbon source (Pandey & Sassetti, 2008; Lee et al, 2013; Bonds & Sampson, 2018). Recent evidence shows that Mtb degrades host cell cholesterol during persistence (Pandey & Sassetti, 2008; Wipperman et al, 2014) and that the inhibition of cholesterol degradation could provide a potential route to control the growth of Mtb in macrophages (VanderVen et al, 2015)
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