Probing molecular mechanisms of M13 bacteriophage adhesion

M13 bacteriophages can provide a versatile platform for nanobiotechnology because of their unique biological and physicochemical properties. Polypeptides on their surfaces can be finely tuned on demand through genetic engineering, enabling tailored assembly of multiple functional components through specific interactions. Their versatility has been demonstrated by synthesizing various unprecedented hybrid materials for energy storage, biosensing, and catalysis. Here we select a specific type of genetically engineered M13 bacteriophage (DSPH) to investigate the origin of interactions. The interaction forces between the phage-coated surface and five different functionalized self-assembled monolayers are directly measured using a surface forces apparatus. We confirm that the phages have strong adhesion energies in acidic environments due to ??-?? stacking and hydrophobic interactions, while hydrogen bonding interactions remain relatively weak. These results provide quantitative and qualitative information of the molecular interaction mechanisms of DSPH phages, which can be utilized as a database of the bacteriophage interactions

Hydrophobic interaction and patch charge attraction in α-Al2O3 dispersions under the influence of adsorbed low molecular-weight polyacrylic acid sodium salt and poly(methacrylic acid) sodium salt: yield stress and AFM force study

© 2016, Springer-Verlag Berlin Heidelberg.Maximum yield stress data showed that low molecular-weight (Mw) (~7 kDa) poly(methacrylic acid) sodium salt (PMA-Na) additive at low surface coverage displayed significant patch charge attraction in contrast to polyacrylic acid sodium salt (PAA-Na) additive of similar Mw and surface coverage. Intramolecular hydrophobic interaction between CH3 groups in the polymer molecule during adsorption produced a much more compact patch with a higher negative charge density giving rise to the stronger patch charge attraction. At high surface coverage, intermolecular hydrophobic interaction between CH3 groups on the adsorbed layer of the interacting particles was not observed from maximum yield stress data. Such interaction was, however, observed in AFM force-distance characterization data for interaction between spherical alumina particles and sapphire plates coated with PMA-Na in retraction mode. The compression of the adsorbed layers at contact during the approach mode was postulated to deform and breakup the intramolecular interaction between the CH3 groups and promoted intermolecular interaction between these groups in the layer coating the particle and plate. This resulted in a strong adhesion force seen in the retraction mode after contact at low pH near the point of zero charge

Measuring protein isoelectric points by AFM-based force spectroscopy using trace amounts of sample

Protein charge at various pH and isoelectric point (pI) values is important in understanding protein function. However, often only trace amounts of unknown proteins are available and pI measurements cannot be obtained using conventional methods. Here, we show a method based on the atomic force microscope (AFM) to determine pI using minute quantities of proteins. The protein of interest is immobilized on AFM colloidal probes and the adhesion force of the protein is measured against a positively and a negatively charged substrate made by layer-by-layer deposition of polyelectrolytes. From the AFM force–distance curves, pI values with an estimated accuracy of ±0.25 were obtained for bovine serum albumin, myoglobin, fibrinogen and ribonuclease A over a range of 4.7–9.8. Using this method, we show that the pI of the ‘footprint’ of the temporary adhesive proteins secreted by the barnacle cyprid larvae of Amphibalanus amphitrite is in the range 9.6–9.7