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Mycobacterium tuberculosis lipoprotein LprG binds lipoarabinomannan and determines its cell envelope localization to control phagolysosomal fusion.

Shukla S, Richardson ET, Athman JJ, Shi L, Wearsch PA, McDonald D, Banaei N, Boom WH, Jackson M, Harding CV - PLoS Pathog. (2014)

Bottom Line: We report that LprG expressed in Mtb binds to lipoglycans, such as lipoarabinomannan (LAM), that mediate Mtb immune evasion.Lipoglycan binding to LprG was dependent on both insertion of lipoglycan acyl chains into a hydrophobic pocket on LprG and a novel contribution of lipoglycan polysaccharide components outside of this pocket.An lprG mutant (Mtb ΔlprG) had lower levels of surface-exposed LAM, revealing a novel role for LprG in determining the distribution of components in the Mtb cell envelope.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Case Western Reserve University/University Hospitals Case Medical Center, Cleveland, Ohio, United States of America.

ABSTRACT
Mycobacterium tuberculosis (Mtb) virulence is decreased by genetic deletion of the lipoprotein LprG, but the function of LprG remains unclear. We report that LprG expressed in Mtb binds to lipoglycans, such as lipoarabinomannan (LAM), that mediate Mtb immune evasion. Lipoglycan binding to LprG was dependent on both insertion of lipoglycan acyl chains into a hydrophobic pocket on LprG and a novel contribution of lipoglycan polysaccharide components outside of this pocket. An lprG mutant (Mtb ΔlprG) had lower levels of surface-exposed LAM, revealing a novel role for LprG in determining the distribution of components in the Mtb cell envelope. Furthermore, this mutant failed to inhibit phagosome-lysosome fusion, an immune evasion strategy mediated by LAM. We propose that LprG binding to LAM facilitates its transfer from the plasma membrane into the cell envelope, increasing surface-exposed LAM, enhancing cell envelope integrity, allowing inhibition of phagosome-lysosome fusion and enhancing Mtb survival in macrophages.

No MeSH data available.


Related in: MedlinePlus

Deacylated ManLAM and LM retain binding to LprG at reduced levels.Binding to LprG was assessed as in Fig. 2 for (A) deacylated LM and (B) deacylated ManLAM. Results are from one experiment and representative of at least three independent experiments.
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ppat-1004471-g004: Deacylated ManLAM and LM retain binding to LprG at reduced levels.Binding to LprG was assessed as in Fig. 2 for (A) deacylated LM and (B) deacylated ManLAM. Results are from one experiment and representative of at least three independent experiments.

Mentions: To further analyze the relative contributions of acyl and non-acyl structures of substrates to LprG binding, we subjected LM and ManLAM to alkaline deacylation. Deacylated LM and deacylated ManLAM both bound specifically to LprG (Fig. 4A and B, Table 2), and this binding was similar for LprG and LprG-V91W. This confirms that non-acyl structures of lipoglycans bind to a site on LprG different from the hydrophobic pocket. In support of this conclusion, loss of the acyl chains reduced the affinities of LM and ManLAM for LprG to values similar to the affinities of acylated LM and acylated ManLAM for LprG-V91W. Deacylation had little effect on the association rate for LM or ManLAM binding to LprG or LprG-V91W but resulted in increased dissociation rates with LprG. Overall, these results establish that Mtb lipoglycans and glycolipids bind to LprG via at least two different interactions at different sites on LprG, one being the acyl chain binding in the hydrophobic pocket and the other being interaction of saccharide chains (likely mannose chains) with LprG outside of the hydrophobic pocket. The ability of LprG to discriminate different glycolipids/lipoglycans based on differences in their saccharide structures may allow differential binding and release of different glycolipids/lipoglycans.


Mycobacterium tuberculosis lipoprotein LprG binds lipoarabinomannan and determines its cell envelope localization to control phagolysosomal fusion.

Shukla S, Richardson ET, Athman JJ, Shi L, Wearsch PA, McDonald D, Banaei N, Boom WH, Jackson M, Harding CV - PLoS Pathog. (2014)

Deacylated ManLAM and LM retain binding to LprG at reduced levels.Binding to LprG was assessed as in Fig. 2 for (A) deacylated LM and (B) deacylated ManLAM. Results are from one experiment and representative of at least three independent experiments.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4214796&req=5

ppat-1004471-g004: Deacylated ManLAM and LM retain binding to LprG at reduced levels.Binding to LprG was assessed as in Fig. 2 for (A) deacylated LM and (B) deacylated ManLAM. Results are from one experiment and representative of at least three independent experiments.
Mentions: To further analyze the relative contributions of acyl and non-acyl structures of substrates to LprG binding, we subjected LM and ManLAM to alkaline deacylation. Deacylated LM and deacylated ManLAM both bound specifically to LprG (Fig. 4A and B, Table 2), and this binding was similar for LprG and LprG-V91W. This confirms that non-acyl structures of lipoglycans bind to a site on LprG different from the hydrophobic pocket. In support of this conclusion, loss of the acyl chains reduced the affinities of LM and ManLAM for LprG to values similar to the affinities of acylated LM and acylated ManLAM for LprG-V91W. Deacylation had little effect on the association rate for LM or ManLAM binding to LprG or LprG-V91W but resulted in increased dissociation rates with LprG. Overall, these results establish that Mtb lipoglycans and glycolipids bind to LprG via at least two different interactions at different sites on LprG, one being the acyl chain binding in the hydrophobic pocket and the other being interaction of saccharide chains (likely mannose chains) with LprG outside of the hydrophobic pocket. The ability of LprG to discriminate different glycolipids/lipoglycans based on differences in their saccharide structures may allow differential binding and release of different glycolipids/lipoglycans.

Bottom Line: We report that LprG expressed in Mtb binds to lipoglycans, such as lipoarabinomannan (LAM), that mediate Mtb immune evasion.Lipoglycan binding to LprG was dependent on both insertion of lipoglycan acyl chains into a hydrophobic pocket on LprG and a novel contribution of lipoglycan polysaccharide components outside of this pocket.An lprG mutant (Mtb ΔlprG) had lower levels of surface-exposed LAM, revealing a novel role for LprG in determining the distribution of components in the Mtb cell envelope.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Case Western Reserve University/University Hospitals Case Medical Center, Cleveland, Ohio, United States of America.

ABSTRACT
Mycobacterium tuberculosis (Mtb) virulence is decreased by genetic deletion of the lipoprotein LprG, but the function of LprG remains unclear. We report that LprG expressed in Mtb binds to lipoglycans, such as lipoarabinomannan (LAM), that mediate Mtb immune evasion. Lipoglycan binding to LprG was dependent on both insertion of lipoglycan acyl chains into a hydrophobic pocket on LprG and a novel contribution of lipoglycan polysaccharide components outside of this pocket. An lprG mutant (Mtb ΔlprG) had lower levels of surface-exposed LAM, revealing a novel role for LprG in determining the distribution of components in the Mtb cell envelope. Furthermore, this mutant failed to inhibit phagosome-lysosome fusion, an immune evasion strategy mediated by LAM. We propose that LprG binding to LAM facilitates its transfer from the plasma membrane into the cell envelope, increasing surface-exposed LAM, enhancing cell envelope integrity, allowing inhibition of phagosome-lysosome fusion and enhancing Mtb survival in macrophages.

No MeSH data available.


Related in: MedlinePlus