13 research outputs found
Comparative molecular dynamics simulations of the antimicrobial peptide CM15 in model lipid bilayers
Spectroscopic Study of Anchoring Aromatic Residues in Membrane Proteins and Peptides: Applications to Protein Folding and Vesicle Disruption
Spectroscopic and Computational Study of Melittin, Cecropin A, and the Hybrid Peptide CM15
Antimicrobial peptides (AMPs), such as cecropin A from
silk moth,
are key components of the innate immune system. They are effective
defensive weapons against invading pathogens, yet they do not target
host eukaryotic cells. In contrast, peptide toxins, such as honeybee
melittin, are nondiscriminating and target both eukaryotic and prokaryotic
cells. An AMP-toxin hybrid peptide that is composed of cecropin A
and melittin (CM15) improves upon the antimicrobial activity of cecropin
A without displaying the nonspecific, hemolytic properties of melittin.
Here we report fluorescence and UV resonance Raman spectra of melittin,
cecropin A, and CM15 with the goal of elucidating peptide-membrane
interactions that help guide specificity. We have probed the potency
for membrane disruption, local environment and structure of the single
tryptophan residue, backbone conformation near the peptide hinge,
and amide backbone structure of the peptides in lipid environments
that mimic eukaryotic and prokaryotic membranes. These experimental
results suggest that melittin inserts deeply into the bilayer, whereas
cecropin A remains localized to the lipid headgroup region. A surprising
finding is that CM15 is a potent membrane-disruptor despite its largely
unfolded conformation. A molecular dynamics analysis complements these
data and demonstrates the ability of CM15 to associate favorably with
membranes as an unfolded peptide. This combined experimental–computational
study suggests that new models for peptide–membrane interactions
should be considered
Structure-Based Small Molecule Modulation of a Pre-Amyloid State: Pharmacological Enhancement of IAPP Membrane-Binding and Toxicity
Islet amyloid polypeptide (IAPP)
is a peptide hormone whose pathological
self-assembly is a hallmark of the progression of type II diabetes.
IAPP–membrane interactions catalyze its higher-order self-assembly
and also underlie its toxic effects toward cells. While there is great
interest in developing small molecule reagents capable of altering
the structure and behavior of oligomeric, membrane-bound IAPP, the
dynamic and heterogeneous nature of this ensemble makes it recalcitrant
to traditional approaches. Here, we build on recent insights into
the nature of membrane-bound states and develop a combined computational
and experimental strategy to address this problem. The generalized
structural approach efficiently identified diverse compounds from
large commercial libraries with previously unrecognized activities
toward the gain-of-function behaviors of IAPP. The use of appropriate
computational prescreening reduced the experimental burden by orders
of magnitude relative to unbiased high-throughput screening. We found
that rationally targeting experimentally derived models of membrane-bound
dimers identified several compounds that demonstrate the remarkable
ability to enhance IAPP–membrane binding and one compound that
enhances IAPP-mediated cytotoxicity. Taken together, these findings
imply that membrane binding <i>per se</i> is insufficient
to generate cytotoxicity; instead, enhanced sampling of rare states
within the membrane-bound ensemble may potentiate IAPP’s toxic
effects
Peptide Amyloid Surface Display
Homomeric self-assembly of peptides
into amyloid fibers is a feature of many diseases. A central role
has been suggested for the lateral fiber surface affecting gains of
toxic function. To investigate this, a protein scaffold that presents
a discrete, parallel β-sheet surface for amyloid subdomains
up to eight residues in length has been designed. Scaffolds that present
the fiber surface of islet amyloid polypeptide (IAPP) were prepared.
The designs show sequence-specific surface effects apparent in that
they gain the capacity to attenuate rates of IAPP self-assembly in
solution and affect IAPP-induced toxicity in insulin-secreting cells