Investigating the interaction patterns at nano-bio interface is a key challenge for safe use of nanoparticles (NPs) to any biological system. The study intends to explore the role of interaction pattern at the iron oxide nanoparticle (IONP)-bacteria interface affecting antimicrobial propensity of IONP. To this end, IONP with magnetite like atomic arrangement and negative surface potential (n-IONP) was synthesized by co-precipitation method. Positively charged chitosan molecule coating was used to reverse the surface potential of n-IONP, i.e. positive surface potential IONP (p-IONP). The comparative data from fourier transform infrared spectroscope, XRD, and zeta potential analyzer indicated the successful coating of IONP surface with chitosan molecule. Additionally, the nanocrystals obtained were found to have spherical size with 10–20 nm diameter. The BacLight fluorescence assay, bacterial growth kinetic and colony forming unit studies indicated that n-IONP (<50 μM) has insignificant antimicrobial activity against Bacillus subtilis and Escherichia coli. However, coating with chitosan molecule resulted significant increase in antimicrobial propensity of IONP. Additionally, the assay to study reactive oxygen species (ROS) indicated relatively higher ROS production upon p-IONP treatment of the bacteria. The data, altogether, indicated that the chitosan coating of IONP result in interface that enhances ROS production, hence the antimicrobial activity.

The work investigates the role of interfacial potential in defining antimicrobial propensity of ZnO nanoparticle (ZnONP) against different Gram positive and Gram negative bacteria. ZnONPs with positive and negative surface potential are tested against different bacteria with varying surface potentials, ranging −14.7 to −23.6 mV. Chemically synthesized ZnONPs with positive surface potential show very high antimicrobial propensity with minimum inhibitory concentration of 50 and 100 μg/mL for Gram negative and positive bacterium, respectively. On other hand, ZnONPs of the same size but with negative surface potential show insignificant antimicrobial propensity against the studied bacteria. Unlike the positively charged nanoparticles, neither Zn2+ ion nor negatively charged ZnONP shows any significant inhibition in growth or morphology of the bacterium. Potential neutralization and colony forming unit studies together proved adverse effect of the resultant nano-bacterial interfacial potential on bacterial viability. Thus, ZnONP with positive surface potential upon interaction with negative surface potential of bacterial membrane enhances production of the reactive oxygen species and exerts mechanical stress on the membrane, resulting in the membrane depolarization. Our results show that the antimicrobial propensity of metal oxide nanoparticle mainly depends upon the interfacial potential, the potential resulting upon interaction of nanoparticle surface with bacterial membrane.

In type 2 diabetics, the hormone amylin misfolds into amyloid plaques implicated in the destruction of the pancreatic β-cells that make insulin and amylin. The aggregative misfolding of amylin is pH-dependent, and exposure of the hormone to acidic and basic environments could be physiologically important. Amylin has two ionizable residues between pH 3 and 9: the α-amino group and His18. Our approach to measuring the pKa values for these sites has been to look at the pH dependence of fibrillization in amylin variants that have only one of the two groups. The α-amino group at the unstructured N-terminus of amylin has a pKa near 8.0, similar to the value in random coil models. By contrast, His18, which is involved in the intermolecular β-sheet structure of the fibrils, has a pKa that is lowered to 5.0 in the fibrils compared to the random coil value of 6.5. The lowered pKa of His18 is due to the hydrophobic environment of the residue, and electrostatic repulsion between positively charged His18 residues on neighboring amylin molecules in the fibril. His18 acts as an electrostatic switch inhibiting fibrillization in its charged state. The presence of a charged side chain at position 18 also affects fibril morphology and lowers amylin cytotoxicity toward a MIN6 mouse model of pancreatic β-cells. In addition to the two expected pKa values, we detected an apparent pKa of ~4.0 for the amylin-derived peptide NAc-SNNFGAILSS-NH2, which has no titratable groups. This pKa is due to the pH-induced ionization of the dye thioflavin T. By using alternative methods to follow fibrillization such as the dye Nile Red or turbidimetry, we were able to distinguish between the titration of the dye and groups on the peptide. Large differences in reaction kinetics were observed between the different methods at acidic pH, because of charges on the ThT dye, which hinder fibril formation much like the charges on the protein.

We characterized the interaction of amylin with heparin fragments of defined length, which model the glycosaminoglycan chains associated with amyloid deposits found in type 2 diabetes. Binding of heparin fragments to the positively charged N-terminal half of monomeric amylin depends on the concentration of negatively charged saccharides but is independent of oligosaccharide length. By contrast, amylin fibrillogenesis has a sigmoidal dependence on heparin fragment length, with an enhancement observed for oligosaccharides longer than four monomers and a leveling off of effects beyond 12 monomers. The length dependence suggests that the negatively charged helical structure of heparin electrostatically complements the positively charged surface of the fibrillar amylin cross-␤ structure. Fluorescence resonance energy transfer and total internal reflection fluorescence microscopy experiments indicate that heparin associates with amylin fibrils, rather than enhancing fibrillogenesis catalytically. Short heparin fragments containing two-or eight-saccharide monomers protect against amylin cytotoxicity toward a MIN6 mouse cell model of pancreatic ␤-cells.Type 2 diabetes accounts for ϳ90% of adult diabetes. The disease currently affects 200 million people worldwide, and its incidence is projected to rise to 300 million by 2025 (1). Like many complex diseases, type 2 diabetes has multifactorial origins (1-4). The disease is characterized by insulin resistance, which causes the pancreas to synthesize more of the hormones insulin and amylin (5). The late stages of the disease are associated with ␤-cell dysfunction and a loss of ␤-cell mass (3, 5).Amylin (also known as islet amyloid polypeptide) is a 37-residue (4-KDa) endocrine hormone that is synthesized by pancreatic ␤-cells and co-secreted with insulin. In its normal state, amylin works together with insulin to control blood sugar (5). Additional amylin functions include suppressing appetite, slowing down the emptying of the stomach, and inhibiting glucagon secretion (5, 6). Like some 30 other polypeptides associated with human amyloid pathologies (6), amylin can undergo aggregative misfolding into fibrils with a cross-␤ structure (5,7,8). Although it is still uncertain whether fibrils or soluble oligomeric precursors are responsible for adverse affects (8 -12), extracellular amylin aggregates have been implicated in the destruction of pancreatic ␤-cells during the progression of type 2 diabetes (5, 9, 13). Amylin is the main component of fibrillar amyloid deposits found in the interstitial fluid between pancreatic islet cells of type 2 diabetes patients tested post-mortem (3,5,14), and extracellular aggregates of amylin are toxic when added to cultures of ␤-cells (9, 13). Overexpression of human amylin has been found to correlate with ␤-cell apoptosis and diabetes-like symptoms in several transgenic mouse and rat models whose endogenous amylin does not fibrillize (15). Genetic evidence that amylin is involved in pathology comes from the familial S20G mutation, which leads...

Nisin inhibits bacterial growth by generating pores in cell membrane and interrupting cell-wall biosynthesis through specific lipid II interaction. However, the role of the hinge region and C-terminus residues of the peptide in antibacterial action of nisin is largely unknown. Here, using molecular dynamics simulations and experimental approach, we report that at high concentration regimes of nisin, interaction with phospholipids may equally deform the bacterial cell membranes even under significantly varying amounts of lipid-II. Membrane thinning, destabilization and decrease in lipid density depend on the degree of oligomerization of nisin. Growth kinetics of Bacillus subtilis and Escherichia coli interestingly show recovery by extended lag phase under low concentrations of nisin treatment while high concentrations of nisin caused decrease in cell viability as recorded by striking reduction in membrane potential and surface area. The significant changes in the dipole potential and fluorescence anisotropy were observed in negatively charged membranes in the absence of lipid-II with increasing concentration of nisin. The identical correlation of cell viability, membrane potential dissipation and morphology with the concentration regime of nisin, in both Bacillus subtilis (lipid II rich) and Escherichia coli (lipid II impoverished), hints at a non-specific physical mechanism where degree of membrane deformation depends on degree of crowding and oligomerization of nisin.

Islet amyloid polypeptide (a.k.a. IAPP, amylin) is a 37 amino acid hormone that has long been associated with the progression of type II diabetes mellitus (TIIDM) disease. The endocrine peptide hormone aggregatively misfolds to form amyloid deposits in and around the pancreatic islet β-cells that synthesize both insulin and IAPP, leading to a decrease in β-cell mass in patients with the disease. Extracellular IAPP amyloids induce β-cell death through the formation of reactive oxygen species, mitochondrial dysfunction, chromatin condensation, and apoptotic mechanisms, although the precise roles of IAPP in TIIDM are yet to be established. Here we review aspects of the normal physiological function of IAPP in glucose regulation together with insulin, and its misfolding which contributes to TIIDM, and may also play roles in other pathologies such as Alzheimer's and heart disease. We summarize information on expression of the IAPP gene, the regulation of the hormone by post-translational modifications, the structural properties of the peptide in various states, the kinetics of misfolding to amyloid fibrils, and the interactions of the peptide with insulin, membranes, glycosaminoglycans, and nanoparticles. Finally, we describe how basic research is starting to have a positive impact on the development of approaches to circumvent IAPP amyloidogenesis. These include therapeutic strategies aimed at stabilizing non-amyloidogenic states, inhibition of amyloid growth or disruption of amyloid fibrils, antibodies directed towards amyloid structures, and inhibition of interactions with cofactors that facilitate aggregation or stabilize amyloids.

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