Protein crystal regulation and harvest via electric field-based method

On-the-fly resolution enhancement in X-ray protein crystallography using electric field

X-ray crystallography has tremendously served structural biology by routinely providing high-resolution 3D structures of macromolecules. The extent of information encoded in the X-ray crystallography is proportional to which resolution the crystals diffract and the structure can be refined to. Therefore, there is a continuous effort to obtain high-quality crystals, especially for those proteins, which are considered difficult to crystallize into high-quality protein crystals of suitable sizes for X-ray crystallography. Efforts in enhancing the resolution in X-ray crystallography have also been made by optimizing crystallization protocols using external stimuli such as an electric field and magnetic field during the crystallization. Here, we present the feasibility of on-the-fly post-crystallization resolution enhancement of the protein crystal diffraction by applying a high-voltage electric field. The electric field between 2 and 11 kV/cm, which was applied after mounting the crystals in the beamline, resulted in the enhancement of the resolution. The crystal diffraction quality improved progressively with the exposure time. Moreover, we also find that upto defined electric field threshold, the protein structure remains largely unperturbed, a conclusion further supported by molecular dynamics simulations.

Voltage-calibrated, finely tunable protein assembly

Neuronally triggered phosphorylation drives the calibrated and cyclable assembly of the reflectin signal transducing proteins, resulting in their fine tuning of colours reflected from specialized skin cells in squid for camouflage and communication. In close parallel to this physiological behaviour, we demonstrate for the first time that electrochemical reduction of reflectin A1, used as a surrogate for charge neutralization by phosphorylation, triggers voltage-calibrated, proportional and cyclable control of the size of the protein's assembly. Electrochemically triggered condensation, folding and assembly were simultaneously analysed using in situ dynamic light scattering, circular dichroism and UV absorbance spectroscopies. The correlation of assembly size with applied potential is probably linked to reflectin's mechanism of dynamic arrest, which is controlled by the extent of neuronally triggered charge neutralization and the corresponding fine tuning of colour in the biological system. This work opens a new perspective on electrically controlling and simultaneously observing reflectin assembly and, more broadly, provides access to manipulate, observe and electrokinetically control the formation of intermediates and conformational dynamics of macromolecular systems.