Electric response of multiarm protein crystals.

Abstract

Electric fields can modify protein-protein interactions and thereby influence phase behavior. In lysozyme-sodium thiocyanate solutions, we recently observed shifts in both the crystallization boundary and the liquid-liquid phase separation line under a weak applied field, along with a range of distinct crystal morphologies. Here, we explore how forming protein crystals respond to variations in field frequency and amplitude, focusing on the morphologies of complex, multiarm structures. At constant protein and salt concentrations, the applied field governs both the number and the angular distribution of crystal arms. These features are analyzed through Fourier analysis of microscopy images, revealing cooperative angular ordering among the arms. Based on these observations, we classify three principal multiarm protein crystal (pX) morphologies: flowerlike pX (dominant at high field strengths), triconic pX (appearing nonmonotonically at lower fields), and conic pX (widely observed under low-field conditions). Near the crystallization boundary, field-driven metastable structures such as tubules, clusters, nematic domains, and fibers also occur in response to the field. These findings demonstrate that electric fields effectively steer protein crystallization pathways and provide insight into the mechanisms of various multiarm crystallization.