cyclopropane and/or cyclohexane rings. Such structure of the hydrophobic part of the molecule not only helps the archaea to live at high temperatures, but also protects their membranes from harmful influence of various phospholipases, secreted by other organisms, and from oxidative stress. However, the role of the branched chain structure in the permeability of archaeal membranes to various ions, gases and water is still an open question. Pores, being conducting defects in a membrane, are the one of the most general causes of loss of membrane barrier function leading to cell death. So structural peculiarities of archaeal lipid should have some influence on membrane resistance to pore formation. We have studied process of pore formation in bilayer lipid membranes formed by ether and ester branched and unbranched lipids using electrical breakdown technique and molecular dynamics simulations. We have shown that branched lipid tails have a great influence on probability of pore formation and dynamics of its growth. A theoretical model connecting pore edge line tension and dynamics of pore widening was proposed. 1204-Pos Board B155Effect of Electrostatic Repulsion on DMPG Bilayers It is well known that ionic strength plays a fundamental role in the structure of DMPG (dimyristoyl phosphatidylglycerol) anionic vesicles in water medium. In buffer, at pH values above 4 and at high ionic strength (above~100 mM), the morphology of DMPG vesicles are rather similar to that of DMPC (dimyristoyl phosphatidylcholine) vesicles. However, at low ionic strength (~4 mM), DMPG dispersions display several anomalous characteristics, which were interpreted as the opening of bilayer pores along the wide bilayer gel-fluid transition region (from~18 o C to 30 o C) 1 . Here, we revisit DMPG in pure water 2 , to emphasize electrostatic interactions between the polar head-groups, which will not be shielded by ions in solution. For comparison, we used several techniques that have been recently applied to DMPG in buffer: light scattering, both static (SLS) and dynamic (DLS); differential scanning calorimetry (DSC); electron spin resonance (ESR) of spin labels incorporated into the aggregates; and viscosity, turbidity and electrical conductivity measurements. DSC and spin labels indicate that, in water, the bilayer gel-fluid transition is even wider, starting around 10 o C but still ending~30 o C. However, high electric conductivity, high viscosity and low turbidity found only in the gel-fluid transition region for DMPG in buffer, are found at higher temperatures in water, when lipid bilayers are already in the fluid state. Moreover, different from DMPG in buffer, in water, vesicles were found to fuse along the transition region. Data suggest that the strong PG --PGelectrostatic repulsion in water leads not only to pore formation in DMPG bilayers, but also to the opening of the vesicles and vesicle fusion.[1]Enoki,T. A.; Henriques, V. B.; M. T. Lamy, Chem. Electrochemistry is a technique that can be used to detect the contents of neurotransmitter...

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...