9 research outputs found
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Amphotericin forms an extramembranous and fungicidal sterol sponge.
For over 50 years, amphotericin has remained the powerful but highly toxic last line of defense in treating life-threatening fungal infections in humans with minimal development of microbial resistance. Understanding how this small molecule kills yeast is thus critical for guiding development of derivatives with an improved therapeutic index and other resistance-refractory antimicrobial agents. In the widely accepted ion channel model for its mechanism of cytocidal action, amphotericin forms aggregates inside lipid bilayers that permeabilize and kill cells. In contrast, we report that amphotericin exists primarily in the form of large, extramembranous aggregates that kill yeast by extracting ergosterol from lipid bilayers. These findings reveal that extraction of a polyfunctional lipid underlies the resistance-refractory antimicrobial action of amphotericin and suggests a roadmap for separating its cytocidal and membrane-permeabilizing activities. This new mechanistic understanding is also guiding development of what are to our knowledge the first derivatives of amphotericin that kill yeast but not human cells
C2′-OH of Amphotericin B Plays an Important Role in Binding the Primary Sterol of Human Cells but Not Yeast Cells
Amphotericin B (AmB) is a clinically
vital antimycotic but is limited
by its severe toxicity. Binding ergosterol, independent of channel
formation, is the primary mechanism by which AmB kills yeast, and
binding cholesterol may primarily account for toxicity to human cells.
The leading structural model predicts that the C2′ hydroxyl
group on the mycosamine appendage is critical for binding both sterols.
To test this, the C2′-OH was synthetically deleted, and the
sterol binding capacity of the resulting derivative, C2′deOAmB,
was directly characterized via isothermal titration calorimetry. Surprisingly,
C2′deOAmB binds ergosterol and, within the limits of detection
of this experiment, does not bind cholesterol. Moreover, C2′deOAmB
is nearly equipotent to AmB against yeast but, within the limits of
detection of our assays, is nontoxic to human cells in vitro. Thus,
the leading structural model for AmB/sterol binding interactions is
incorrect, and C2′deOAmB is an exceptionally promising new
antifungal agent
C2′-OH of Amphotericin B Plays an Important Role in Binding the Primary Sterol of Human Cells but Not Yeast Cells
Amphotericin B (AmB) is a clinically
vital antimycotic but is limited
by its severe toxicity. Binding ergosterol, independent of channel
formation, is the primary mechanism by which AmB kills yeast, and
binding cholesterol may primarily account for toxicity to human cells.
The leading structural model predicts that the C2′ hydroxyl
group on the mycosamine appendage is critical for binding both sterols.
To test this, the C2′-OH was synthetically deleted, and the
sterol binding capacity of the resulting derivative, C2′deOAmB,
was directly characterized via isothermal titration calorimetry. Surprisingly,
C2′deOAmB binds ergosterol and, within the limits of detection
of this experiment, does not bind cholesterol. Moreover, C2′deOAmB
is nearly equipotent to AmB against yeast but, within the limits of
detection of our assays, is nontoxic to human cells in vitro. Thus,
the leading structural model for AmB/sterol binding interactions is
incorrect, and C2′deOAmB is an exceptionally promising new
antifungal agent
Recommended from our members
Amphotericin forms an extramembranous and fungicidal sterol sponge.
For over 50 years, amphotericin has remained the powerful but highly toxic last line of defense in treating life-threatening fungal infections in humans with minimal development of microbial resistance. Understanding how this small molecule kills yeast is thus critical for guiding development of derivatives with an improved therapeutic index and other resistance-refractory antimicrobial agents. In the widely accepted ion channel model for its mechanism of cytocidal action, amphotericin forms aggregates inside lipid bilayers that permeabilize and kill cells. In contrast, we report that amphotericin exists primarily in the form of large, extramembranous aggregates that kill yeast by extracting ergosterol from lipid bilayers. These findings reveal that extraction of a polyfunctional lipid underlies the resistance-refractory antimicrobial action of amphotericin and suggests a roadmap for separating its cytocidal and membrane-permeabilizing activities. This new mechanistic understanding is also guiding development of what are to our knowledge the first derivatives of amphotericin that kill yeast but not human cells
Amphotericin forms an extramembranous and fungicidal sterol sponge
Amphotericin has remained the powerful but highly toxic last line of defense in treating life-threatening fungal infections in humans for over 50 years with minimal development of microbial resistance. Understanding how this small molecule kills yeast is thus critical for guiding development of derivatives with an improved therapeutic index and other resistance-refractory antimicrobial agents. In the widely accepted ion channel model for its mechanism of cytocidal action, amphotericin forms aggregates inside lipid bilayers that permeabilize and kill cells. In contrast, we report that amphotericin exists primarily in the form of large, extramembranous aggregates that kill yeast by extracting ergosterol from lipid bilayers. These findings reveal that extraction of a polyfunctional lipid underlies the resistance-refractory antimicrobial action of amphotericin and suggests a roadmap for separating its cytocidal and membrane-permeabilizing activities. This new mechanistic understanding is also guiding development of the first derivatives of amphotericin that kill yeast but not human cells