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PDBsum entry 2b5k
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Antimicrobial protein
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PDB id
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2b5k
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References listed in PDB file
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Key reference
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Title
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Solution structure and interaction of the antimicrobial polyphemusins with lipid membranes.
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Authors
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J.P.Powers,
A.Tan,
A.Ramamoorthy,
R.E.Hancock.
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Ref.
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Biochemistry, 2005,
44,
15504-15513.
[DOI no: ]
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PubMed id
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Abstract
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The horseshoe crab cationic antimicrobial peptide polyphemusin I is highly
active in vitro but not protective in mouse models of bacterial and LPS
challenge, while a synthetic polyphemusin variant, PV5, was previously shown to
be protective in vivo. In this study, we investigated the interaction of these
peptides with lipid membranes in an effort to propose a mechanism of
interaction. The solution structure of PV5 was determined by proton NMR in the
absence and presence of dodecylphosphocholine (DPC) micelles. Like polyphemusin
I, PV5 is a beta-hairpin but appeared less amphipathic in solution. Upon
association with DPC micelles, PV5 underwent side chain rearrangements which
resulted in an increased amphipathic conformation. Using fluorescence
spectroscopy, both peptides were found to have limited affinity for neutral
vesicles composed of phosphatidylcholine (PC). Incorporation of 25 mol %
cholesterol or phosphatidylethanolamine into PC vesicles produced little change
in the partitioning of either peptide. Incorporation of 25 mol %
phosphatidylglycerol (PG) into PC vesicles, a simple prokaryotic model, resulted
in a large increase in the affinity for both peptides, but the partition
coefficient for PV5 was almost twice that of polyphemusin I. Differential
scanning calorimetry studies supported the partitioning data and demonstrated
that neither peptide interacted readily with neutral PC vesicles. Both peptides
showed affinity for negatively charged membranes incorporating PG. The affinity
of PV5 was much greater as the pretransition peak was absent at low peptide to
lipid ratios (1:400) and the reduction in enthalpy of the main transition was
greater than that produced by polyphemusin I. Both peptides decreased the
lamellar to inverted hexagonal phase transition temperature of PE indicating the
induction of negative curvature strain. These results, combined with previous
findings that polyphemusin I promotes lipid flip-flop but does not induce
significant vesicle leakage, ruled out the torroidal pore and carpet mechanisms
of antimicrobial action for these polyphemusins.
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