Correlation of an Antimicrobial Peptide's Potency and Its Influences on Membrane Elasticity

Abstract

antimicrobial peptide (AMP) and a scaffold made from elastin-like polypeptide chains. Direct immobilization of AMPs onto a biomaterial surface reduces its bioactivity; in contrast, surface attachment of AMPs via tethers increases bioactivity and enhances stability. We hypothesize that unstructured hydrophilic protein linkers will behave similarly to conventional hydrophilic polymer tethers. Unstructured hydrophilic protein tethers have been designed using atomistic MD simulations and are being tested experimentally. To obtain insight into how the designed protein tether impacts AMP activity, its molecular mechanism must be established. The AMP human cathelicidin LL-37 [1] is known to be in equilibrium between various oligomeric states, ranging from monomers to heptamers. Using the visualization tool VMD, these oligomeric states were modeled starting from the available dimeric LL-37 structure (PDB#:5NNM). The structure prediction server Robetta was employed to predict energetically important amino acid residues (hot spots) involved in protein-protein interfaces of the modeled structures. Molecular Dynamics Flexibility Fitting (MDFF) was utilized with the available PDB structure (PDB#:2YMK) of the hexameric AMP channel dermcidin to fit the hexameric LL-37 structure. The CHARMM GUI membrane builder was subsequently utilized to simulate the membrane around the hexameric structure. Deducing the orientation of the oligomeric structure in the membrane and adding the protein tether [2] allows us to observe its impact on the LL-37-membrane interactions. A complete model of this system will allow the design of unstructured hydrophilic protein tethers, and aid in understanding the effects of these tethers on AMP conformation as well as bacterial toxicity.[1] K.Host-defense peptides (HDPs) play an integral role in the fight against invading pathogens. To fully exploit their potential as prototypes for novel antimicrobials the molecular basis of their mechanism of action, which includes disrupting plasma membranes, must be understood. The host-defense peptides piscidin P1 and piscidin P3, two potent HDPs isolated from striped bass, display strong antimicrobial activities against a large number of Gram-positive and -negative bacteria, including methicillin-resistant S. aureus (MRSA), viruses such as HIV-1, fungi, yeasts, and cancer cells. The two 22-residue, helical, cationic peptides differ only slightly in amino-acid sequences, but P1 is more potent than P3. Solid state NMR showed that P1 and P3 adopt a very similar helical structure in fluid lipid membranes. However, neutron diffraction and reflectometry, in conjunction with electrical impedance spectroscopy (EIS) and surface plasmon resonance (SPR) measurements reveal differing conformations of the two peptides in membrane, depending on lipid composition and peptide metalation state (Ni2þ or Cu2þ bound to the N-terminal ATCUN motif). These findings offer new insights on the structural interactions of the peptides with membranes at the molecular level. The contrasting behav...