Dual role of isocitrate lyase 1 in the glyoxylate and methylcitrate cycles in Mycobacterium tuberculosis

Abstract

SummaryThe role of isocitrate lyase (ICL) in the glyoxylate cycle and its necessity for persistence and virulence of Mycobacterium tuberculosis has been well described. Recent reports have alluded to an additional role for this enzyme in M. tuberculosis metabolism, specifically for growth on propionate. A product of b-oxidation of odd-chain fatty acids is propionyl-CoA. Clearance of propionyl-CoA and the by-products of its metabolism via the methylcitrate cycle is vital due to their potentially toxic effects. Although the genome of M. tuberculosis encodes orthologues of two of the three enzymes of the methylcitrate cycle, methylcitrate synthase and methylcitrate dehydratase, it does not appear to contain a distinct 2-methylisocitrate lyase (MCL). Detailed structural analysis of the MCL from Escherichia coli suggested that the differences in substrate specificity between MCLs and ICLs could be attributed to three conserved amino acid substitutions in the active site, suggesting an MCL signature. However, here we provide enzymatic evidence that shows that despite the absence of the MCL signature, ICL1 from M. tuberculosis can clearly function as a MCL. Furthermore, the crystal structure of ICL1 with pyruvate and succinate bound demonstrates that the active site can accommodate the additional methyl group without significant changes to the structure.

Isocitrate lyase mediates broad antibiotic tolerance in Mycobacterium tuberculosis

“…Mtb's ICLs serve dual roles in the glyoxylate shunt and methylcitrate cycles, pathways that play canonical roles in metabolism of even and odd chain fatty acids and/or branched chain ketoacids, respectively. Mtb's ICLs have further been shown to be essential for both establishment and maintenance of infection in mice [17][18][19] . However, our studies, were conducted in the absence of a fatty acid carbon source, and thus suggested a non-canonical metabolic role for Mtb's ICL in its response to antibiotic exposure.…”

Genomic versatility and functional variation between two dominant heterotrophic symbionts of deep-sea Osedax worms

“…Comparative genomics of Osedax symbionts SK Goffredi et al pathogens including Mycobacterium and Salmonella, presumably by allowing for rapid and efficient growth on host-produced odd-chain-length fatty acids (McKinney et al, 2000;Fang et al, 2005;Muñ oz-Elías and McKinney 2005;Gould et al, 2006;Eisenreich et al, 2010). The Osedax symbionts possess many genes devoted to the specific degradation of branched-chain amino acids, which also results in the generation of propionyl-CoA, rather than acetyl-CoA (Muñ oz-Elías et al, 2006), thus increasing the necessity for the methylcitrate cycle.…”

Role of the methylcitrate cycle in growth, antagonism and induction of systemic defence responses in the fungal biocontrol agent Trichoderma atroviride

“…The main difference between the two enzymes is the replacement of conserved amino acid residues phenylalanine and threonine in the ICL active site by leucine and serine in MCL (Brock, 2005;Müller et al, 2011). This two amino acid replacement allows acceptance of an additional methyl group in MCL (Liu et al, 2005;Gould et al, 2006). In our study, the active site of T. atroviride MCL contains leucine and serine, which indicates MCL activity.…”

“…In spite of the similarity, ICL and MCL in filamentous fungi have unique substrate specificities and catalytic motifs (Brock, 2005;Müller et al, 2011), and thus perform non-overlapping functions in their respective pathways (Brock et al, 2001;Brock, 2005). In contrast to that, studies in M. tuberculosis, M. smegmatis and Saccharomyces cerevisiae suggest a dual role of ICL: as ICL in the glyoxylate cycle, as MCL in the methylcitrate cycle and jointly required for acetate and propionate metabolism, growth and virulence (Gould et al, 2006;Muñoz-Elías & McKinney, 2005;Upton & McKinney, 2007). The situation is more complicated in the phytopathogenic fungus Fusarium graminearum, where ICL and MCL perform specific roles in acetate and propionate metabolism, respectively; however, both enzymes have redundant functions for plant infection (Lee et al, 2009).…”

“…There are several reports that show the unique function of ICL and MCL in their respective pathways (Brock et al, 2001;Brock, 2005;Liu et al, 2005). However, a dual role of ICL is shown in the bacteria M. tuberculosis and M. smegmatis, and the yeast S. cerevisiae (Gould et al, 2006;Muñoz-Elías & McKinney, 2005;Upton & McKinney, 2007). Furthermore, MCS activity from As.…”