Polyhedral Instability of Glucose Isomerase Crystals

The problem of polyhedral (in)stability for the crystallization of macromolecules is discussed. We present both qualitative and quantitative data on the transition of face morphology in response to surface concentration gradients for the case of glucose isomerase. We show that in the absence of convective currents an isotropic protein depletion zone (PDZ) is installed. The mismatch between the spherical shape of the PDZ and the crystal habit leads to the Berg effect which gives rise to a localization of two-dimensional nucleation near the vertices and a retardation of step advancement at the center of the face. In response to this supersaturation inconstancy, a stabilizing microcompensation profile is setup that changes the local face kinetic constant β. Upon attaining a critical slope, β reaches its maximum and the destabilizing mechanism, that is, surface protein concentration gradients, leads to the loss of polyhedral stability. Furthermore, we demonstrate that polyhedral instability is promoted even further by 0.1% agarose.