Mycolactone subverts immunity by selectively blocking the Sec61 translocon

Abstract

Baron et al. show that mycolactone, an immunosuppressive macrolide produced by the pathogen Mycobacterium ulcerans, operates by targeting the Sec61 translocon. This identifies the most potent Sec61 inhibitor reported to date and the potential of inhibiting Sec61 for immune modulation.

Sec61 blockade by mycolactone inhibits antigen cross-presentation independently of endosome-to-cytosol export

“…In contrast to previously described Sec61 inhibitors, such as cotransin (18), mycolactone prevents the biogenesis of secretory and transmembrane proteins with minor selectivity toward Sec61 substrates, as well as uniformly high efficacy (13,16). Single-amino acid mutagenesis localized its binding site on the luminal side of the translocon, near the plug domain that occludes Sec61 in its inactive state (13). Mycolactone allows acute blockade of Sec61, and we used it in the present study to examine the direct contribution of this channel to antigen cross-presentation, endosome-to-cytosol export, and ER-tocytosol export.…”

“…β-Galactosidase levels were quantified using a colorimetric substrate, chlorophenol red-β-D-galactopyranoside (CPRG). To ensure that B3Z activation itself was not affected by mycolactone, we used a B3Z line expressing the R66G mycolactone-resistant mutant of Sec61 (Sec61-R66G), generated as described (13). We observed no difference in the efficiency of OVA cross-presentation or in the capacity of DCs to activate T cells when incubated directly with the OVA 257-264 peptide (Fig.…”

“…Mycolactone is a polyketidederived macrolide produced by the human pathogen Mycobacterium ulcerans, which was recently identified as a potent Sec61 inhibitor (13)(14)(15)(16). Mycolactone diffuses passively across the plasma membrane to target the pore-forming subunit of the translocon (Sec61α) (13), leading to the proteasomal degradation of newly synthesized Sec61 clients blocked in translocation (17).…”

“…Mycolactone is a polyketidederived macrolide produced by the human pathogen Mycobacterium ulcerans, which was recently identified as a potent Sec61 inhibitor (13)(14)(15)(16). Mycolactone diffuses passively across the plasma membrane to target the pore-forming subunit of the translocon (Sec61α) (13), leading to the proteasomal degradation of newly synthesized Sec61 clients blocked in translocation (17). In contrast to previously described Sec61 inhibitors, such as cotransin (18), mycolactone prevents the biogenesis of secretory and transmembrane proteins with minor selectivity toward Sec61 substrates, as well as uniformly high efficacy (13,16).…”

“…Mycolactone diffuses passively across the plasma membrane to target the pore-forming subunit of the translocon (Sec61α) (13), leading to the proteasomal degradation of newly synthesized Sec61 clients blocked in translocation (17). In contrast to previously described Sec61 inhibitors, such as cotransin (18), mycolactone prevents the biogenesis of secretory and transmembrane proteins with minor selectivity toward Sec61 substrates, as well as uniformly high efficacy (13,16). Single-amino acid mutagenesis localized its binding site on the luminal side of the translocon, near the plug domain that occludes Sec61 in its inactive state (13).…”