Antimicrobial Peptide Mimicking Primary Amine and Guanidine Containing Methacrylamide Copolymers Prepared by Raft Polymerization.

Naturally occurring antimicrobial peptides (AMPs) display the ability to eliminate a wide variety of bacteria, without toxicity to the host eukaryotic cells. Synthetic polymers containing moieties mimicking lysine and arginine components found in AMPs have been reported to show effectiveness against specific bacteria, with the mechanism of activity purported to depend on the nature of the amino acid mimic. In an attempt to incorporate the antimicrobial activity of both amino acids into a single water-soluble copolymer, a series of copolymers containing lysine mimicking aminopropyl methacrylamide (APMA) and arginine mimicking guanadinopropyl methacrylamide (GPMA) were prepared via aqueous RAFT polymerization. Copolymers were prepared with varying ratios of the comonomers, with degree of polymerization of 35-40 and narrow molecular weight distribution to simulate naturally occurring AMPs. Antimicrobial activity was determined against Gram-negative and Gram-positive bacteria under conditions with varying salt concentration. Toxicity to mammalian cells was assessed by hemolysis of red blood cells and MTT assays of MCF-7 cells. Antimicrobial activity was observed for APMA homopolymer and copolymers with low concentrations of GPMA against all bacteria tested, with low toxicity toward mammalian cells.

Kinetics and control of self-assembly of ABH1 hydrophobin from the edible white button mushroom.

Hydrophobins are small fungal proteins that self-assemble at hydrophobic/hydrophilic interfaces to form stable, amyloid membranes that are resistant to denaturation. Their remarkable surface activity has driven intense research for their potential utility in biomedical and cosmetic applications. In this research, the self-assembly characteristics of the Class I hydrophobin ABH1 from Agaricus bisporus , the edible white button mushroom, were evaluated as a function of solution and interface properties, in an attempt to gain greater mechanistic understanding. The kinetics of self-assembly were examined using dynamic quartz crystal microbalance techniques in combination with AFM, ellipsometry, contact angle goniometry, light scattering, and circular dichroism spectroscopy. It was found that the strength of interfacial tension between two phases drives the speed of ABH1 assembly and that the nature and location of the molecular ordering was influenced by temperature. ABH1 demonstrates different characteristics and self-assembly properties than those reported for other Class I hydrophobins, including causing an instantaneous decrease in surface tension in aqueous solution and undergoing a direct transition to ß-sheet conformation on self-assembly at elevated temperature.

Antimicrobial poly(methacrylamide) derivatives prepared via aqueous RAFT polymerization exhibit biocidal efficiency dependent upon cation structure.

Antimicrobial peptides (AMPs) show great potential as alternative therapeutic agents to conventional antibiotics as they can selectively bind and eliminate pathogenic bacteria without harming eukaryotic cells. It is of interest to develop synthetic macromolecules that mimic AMPs behavior, but that can be produced more economically at commercial scale. Herein, we describe the use of aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization to prepare primary and tertiary amine-containing polymers with precise molecular weight control and narrow molecular weight distributions. Specifically, N-(3-aminopropyl)methacrylamide (APMA) was statistically copolymerized with N-[3-(dimethylamino)propyl]methacrylamide (DMAPMA) or N-[3-(diethylamino)propyl]methacrylamide (DEAPMA) to afford a range of (co)polymer compositions. Analysis of antimicrobial activity against E. coli (Gram-negative) and B. subtilis (Gram-positive) as a function of buffer type, salt concentration, pH, and time indicated that polymers containing large fractions of primary amine were most effective against both strains of bacteria. Under physiological pH and salt conditions, the polymer with the highest primary amine content caused complete inhibition of bacterial growth at low concentrations, while negligible hemolysis was observed over the full range of concentrations tested, indicating exceptional selectivity. The cytotoxicity of select polymers was evaluated against MCF-7 cells.

Specific soluble oligomers of amyloid-ß peptide undergo replication and form non-fibrillar aggregates in interfacial environments.

Aggregates of amyloid-ß (Aß) peptides have been implicated in the etiology of Alzheimer disease. Among the different forms of Aß aggregates, low molecular weight species ranging between ~2- and 50-mers, also called "soluble oligomers," have emerged as the species responsible for early synaptic dysfunction and neuronal loss. Emerging evidence suggests that the neurotoxic oligomers need not be formed along the obligatory nucleation-dependant fibril formation pathway. In our earlier work, we reported the isolation of one such "off-pathway" 12-18-mer species of Aß42 generated from fatty acids called large fatty acid-derived oligomers (LFAOs) (Kumar, A., Bullard, R. L., Patel, P., Paslay, L. C., Singh, D., Bienkiewicz, E. A., Morgan, S. E., and Rangachari, V. (2011) PLoS One 6, e18759). Here, we report the physiochemical aspects of LFAO-monomer interactions as well as LFAO-LFAO associations in the presence of interfaces. We discovered that LFAOs are a replicating strain of oligomers that recruit Aß42 monomers and quantitatively convert them into LFAO assemblies at the expense of fibrils, a mechanism similar to prion propagation. We also found that in the presence of hexane-buffer or chloroform-buffer interfaces LFAOs are able to associate with themselves to form larger but non-fibrillar aggregates. These results further support the hypothesis that low molecular weight oligomers can be generated via non-fibril formation pathways. Furthermore, the unique replicating property of off-pathway oligomers may hold profound significance for Alzheimer disease pathology.

Non-esterified fatty acids generate distinct low-molecular weight amyloid-ß (Aß42) oligomers along pathway different from fibril formation.

Amyloid-ß (Aß) peptide aggregation is known to play a central role in the etiology of Alzheimer's disease (AD). Among various aggregates, low-molecular weight soluble oligomers of Aß are increasingly believed to be the primary neurotoxic agents responsible for memory impairment. Anionic interfaces are known to influence the Aß aggregation process significantly. Here, we report the effects of interfaces formed by medium-chain (C9-C12), saturated non-esterified fatty acids (NEFAs) on Aß42 aggregation. NEFAs uniquely affected Aß42 aggregation rates that depended on both the ratio of Aß:NEFA as well the critical micelle concentration (CMC) of the NEFAs. More importantly, irrespective of the kind of NEFA used, we observed that two distinct oligomers, 12-18 mers and 4-5 mers were formed via different pathway of aggregation under specific experimental conditions: (i) 12-18 mers were generated near the CMC in which NEFAs augment the rate of Aß42 aggregation towards fibril formation, and, (ii) 4-5 mers were formed above the CMC, where NEFAs inhibit fibril formation. The data indicated that both 12-18 mers and 4-5 mers are formed along an alternate pathway called 'off-pathway' that did not result in fibril formation and yet have subtle structural and morphological differences that distinguish their bulk molecular behavior. These observations, (i) reflect the possible mechanism of Aß aggregation in physiological lipid-rich environments, and (ii) reiterate the fact that all oligomeric forms of Aß need not be obligatory intermediates of the fibril formation pathway.