Lipid-Dependent Bimodal MCL1 Membrane Activity
- Publication date
- 2014
- Publisher
Abstract
Increasing evidence indicates that
the mitochondrial lipid membrane
environment directly modulates the BCL2 family protein function, but
the underlying mechanisms are still poorly understood. Here, we used
minimalistic reconstituted systems to examine the influence of mitochondrial
lipids on MCL1 activity and conformation. Site-directed mutagenesis
and fluorescence spectroscopic analyses revealed that the BCL2 homology
region of MCL1 (MCL1ΔNΔC) inhibits permeabilization of
MOM-like membranes exclusively via canonical BH3-into-groove interactions
with both cBID-like activators and BAX-like effectors. Contrary to
currently popular models, MCL1ΔNΔC did not require becoming
embedded into the membrane to inhibit membrane permeabilization, and
interaction with cBID was more productive for MCL1ΔNΔC
inhibitory activity than interaction with BAX. We also report that
membranes rich in cardiolipin (CL), but not phosphatidylinositol (PI),
trigger a profound conformational change in MCL1ΔNΔC leading
to membrane integration and unleashment of an intrinsic lipidic pore-forming
activity of the molecule. Cholesterol (CHOL) reduces both the conformational
change and the lipidic pore-forming activity of MCL1ΔNΔC
in CL-rich membranes, but it does not affect the interaction of MCL1ΔNΔC
with proapoptotic partners in MOM-like liposomes. In addition, we
identified MCL1α5 as the minimal domain of the protein responsible
for its membrane-permeabilizing function both in model membranes and
at the mitochondrial level. Our results provide novel mechanistic
insight into MCL1 function in the context of a membrane milieu and
add significantly to a growing body of evidence supporting an active
role of mitochondrial membrane lipids in BCL2 protein function