Diffracting crystals of an intrinsically disordered protein (IDP) AtPP16-1 grown in 1.3 V cm−1 DC field

Abstract

DC electric field as weak as ∼1.3 V cm⁻¹ induces crystal nucleation in very dilute protein solutions lacking precipitant. The basis of such growth is the microscopic model of interaction of protein dipoles with the Stark field, leading to glass-like amorphous aggregation and reconfiguration of the aggregates for crystal nucleation. This modest approach is very different from an earlier and rather ‘aggressive’ one in which electric field of ∼1 kV or orders of magnitude in excess is used to influence charge migration in a highly concentrated protein solution having precipitant confined to the crystallization drop. As an application of the precipitant-lacking ultralow protein method, the present work seeks the assistance of internally supplied 1.3 V cm⁻¹ DC field to crystallize an intrinsically disordered protein (IDP) called AtPP16-1 in a 0.017 mg mL⁻¹ solution. Crystallization is allowed in cuvette cells of spectrometers with online electric field, enabling measurement of real time changes in spectral features. The average crystal size increases with the time of passage of the electric field, from ∼0.042 at 10 min to 0.165 µm at the end of 300 min. The cubic crystals diffract electron and X-ray. Electron diffraction spot indexing yields lattice spacing d_hkl ∼ 2.85 Å, consistent with 2.88 Å found from powder X-ray diffraction analysis. This level of lattice spacing will correspond to moderately resolved crystal structure of the IDP.