Micromechanics of Anisotropic Cross-Linked Enzyme Crystals

Catalytic activity of protein crystals correlates with their particle size due to diffusion limitations. However, because the particles need to be restrained during, e.g., a filtration process, keeping a minimum particle size is required. Thus, knowledge of mechanical properties of enzyme crystals is needed for downstream process design in the biopharmaceutical industry to avoid particle breakage. In this study, hardness and Young’s modulus of cross-linked lysozyme crystals and cross-linked halohydrin dehalogenase from Ilumatobacter coccineus (HheG) crystals are evaluated using atomic force microscopy. The results show that hardness of lysozyme and HheG crystals is in the range of 2–22 MPa. For Young’s modulus of lysozyme crystals, values between 40 and 1820 MPa are measured, while HheG crystals ranging between 40 and 1200 MPa, respectively. The results for lysozyme crystals are comparable to those published in the current literature on native protein crystals. Hence, the cross-linking seems not to signif...