The Effect of Macromolecular Crowding, Ionic Strength and Calcium Binding on Calmodulin Dynamics

The flexibility in the structure of calmodulin (CaM) allows its binding to over 300 target proteins in the cell. To investigate the structure-function relationship of CaM, we combined methods of computer simulation and experiments based on circular dichroism (CD) to investigate the structural characteristics of CaM that influence its target recognition in crowded cell-like conditions. We developed a unique multiscale solution of charges computed from quantum chemistry, together with protein reconstruction, coarse-grained molecular simulations, and statistical physics, to represent the charge distribution in the transition from apoCaM to holoCaM upon calcium binding. Computationally, we found that increased levels of macromolecular crowding, in addition to calcium binding and ionic strength typical of that found inside cells, can impact the conformation, helicity and the EF hand orientation of CaM. Because EF hand orientation impacts the affinity of calcium binding and the specificity of CaM's target selection, our results may provide unique insight into understanding the promiscuous behavior of calmodulin in target selection inside cells.Comment: Accepted to PLoS Comp Biol, 201

Versatile Underwater Adhesive with Microarchitecture Triggered by Solvent Exchange

Polyelectrolyte complexation is critical to the formation and properties of many biological and polymeric materials, and is typically initiated by aqueous solution mixing that results in fluid-fluid phase separation, e.g., coacervation. Here we report a versatile and strong wet-contact adhesive inspired by sandcastle worm cement that enables both a triggered complexation of polyelectrolytes, and formation of a porous architecture. A catecholfunctionalized weak poly-anion was premixed with a poly-cation in dimethyl sulfoxide (DMSO). The polymer solution was applied underwater to substrates where electrostatic complexation, phase inversion, and rapid setting were actuated by water-DMSO solvent exchange. This process offers enhanced spatial and temporal control of complexation, thereby fostering rapid (??? 25 s) and robust underwater adhesion (Wad ??? 2 J/m2) of complexed catecholic polyelectrolytes to all tested surfaces including plastics, glasses, metals, and biological surfaces. The solvent exchange process is adaptable to diverse materials chemistry, supporting functionalities well beyond aqueous complex coacervates

In Situ Assembly of Hydrophilic and Hydrophobic Nanoparticles at Oil–Water Interfaces as a Versatile Strategy To Form Stable Emulsions

We report a conceptually new strategy for forming particle-stabilized emulsions. We begin with stable, dilute suspensions of highly hydrophilic nanoparticles in water and hydrophobic nanoparticles in oil. When the two suspensions are mixed, attractive interactions between the hydrophilic and hydrophobic particles cause them to assemble at the oil–water interfaces into partially wettable or Janus-like clusters that effectively stabilize emulsions. By tuning the ratio of hydrophilic to hydrophobic particles in the clusters, both water-in-oil as well as oil-in-water emulsions can be formed. The van der Waals interaction energy between two particle types across an aqueous–organic interface provide a systematic guide to particle and liquid combinations that can form stable emulsions using our strategy, or identify when emulsions will not form. Our experiments and analysis provide a new platform for the formation of particle-stabilized emulsions and can be used to combine particles of different functionalities at emulsion droplet surfaces for generating novel materials