Mycolactone: A Polyketide Toxin from Mycobacterium ulcerans Required for Virulence

Abstract

Mycolactone is the exotoxin produced by Mycobacterium ulcerans and is the virulence factor behind the neglected tropical disease Buruli ulcer. The toxin has a broad spectrum of biological effects within the host organism, stemming from its interaction with at least two molecular targets and the inhibition of protein uptake into the endoplasmic reticulum. Although it has been shown that the toxin can passively permeate into host cells, it is clearly lipophilic. Association with lipid carriers would have substantial implications for the toxin's distribution within a host organism, delivery to cellular targets, diagnostic susceptibility, and mechanisms of patho-genicity. Yet the toxin's interactions with, and distribution in, lipids are unknown. Herein we have used coarse-grained molecular dynamics simulations, guided by all-atom simulations, to study the interaction of mycolactone with pure and mixed lipid membranes. Using established techniques, we calculated the toxin's preferential localization, membrane translocation, and impact on membrane physical and dynamical properties. The computed water-octanol partition coefficient indicates that mycolactone prefers to be in an organic phase rather than in an aqueous environment. Our results show that in a solvated membrane environment the exo-toxin mainly localizes in the water-membrane interface, with a preference for the glycerol moi-ety of lipids, consistent with the reported studies that found it in lipid extracts of the cell. The calculated association constant to the model membrane is similar to the reported association constant for Wiskott-Aldrich syndrome protein. Mycolactone is shown to modify the physical properties of membranes, lowering the transition temperature, compressibility modulus, and critical line tension at which pores can be stabilized. It also shows a tendency to behave as a linactant, a molecule that localizes at the boundary between different fluid lipid domains in membranes and promotes inter-mixing of domains. This property has implications for the tox-in's cellular access, T-cell immunosuppression, and therapeutic potential.

Total synthesis of mycolactones A and B

“…A solution of (+)-Ipc 2 BOMe (21.58 g, 68.2 mmol) in Et 2 O (50 mL) was then added via cannula. The colorless solution was allowed to stir at -78 °C for 30 min, and then BF 3 •Et 2 O (9.5 mL, 75 mmol) was added followed immediately by a solution of aldehyde 26 (9.86 g, 45.6 mmol) in THF (50 mL, 10 mL wash). The solution was stirred at -78 °C for 3 h and then quenched by addition of 3 N NaOH (130 mL).…”

“…The reaction mixture was degassed once and was stirred at room temperature for 15 min and then at 55 °C overnight. The cooled reaction mixture was poured into a mixture of saturated aqueous NaHCO 3 A mixture of CH 2 Cl 2 (200 mL), H 2 O (50 mL) and TFA (12.5 mL) was shaken vigorously. The CH 2 Cl 2 layer (150 mL) was used to dissolve 38 (1.437 g, 2.86 mmol), which was stirred for 5.5 h at room temperature.…”

Suppressive effect of mycolactone-containing fraction from Mycobacterium ulcerans on antibody production against co-administered antigens

“…The pathogenesis of Buruli ulcer depends on mycolactone, a lipid toxin produced by M. ulcerans [4]. Mycolactone is a polyketide-derived macrolide [5] that exerts cytopathic effects on cultured L929 murine fibroblasts [4,6]. Injection of mycolactone into guinea pig produced an ulcer similar to Buruli ulcer [4].…”

“…Mycolactone is a polyketide-derived macrolide [5] that exerts cytopathic effects on cultured L929 murine fibroblasts [4,6]. Injection of mycolactone into guinea pig produced an ulcer similar to Buruli ulcer [4]. Mycolactone inhibits the production of various cytokines, chemokines, and other secreted immune modulators [7] from immune cells such as monocytes [8], macrophages [9], dendritic cells [10], and T cells [11][12][13].…”

“…The disease mainly prevails in West Africa, and its incidence is increasing in Asia, Australia, and Latin America [1][2][3]. The pathogenesis of Buruli ulcer depends on mycolactone, a lipid toxin produced by M. ulcerans [4]. Mycolactone is a polyketide-derived macrolide [5] that exerts cytopathic effects on cultured L929 murine fibroblasts [4,6].…”