Simulation of lysozyme crystal growth by the Monte Carlo method
The main features of the observed crystal growth of the protein lysozyme are reproduced by Monte Carlo simulations based on a simple model. The free parameters of the model are the strengths of the three main types of protein-protein contacts occurring in the P43212 lattice of the tetragonal form of lysozyme and the equilibrium rate of attachment of molecules to lattice sites. The simulated crystal surfaces, like the actual surfaces observed by electron microscopy, display structures characteristic of growth by a two-dimensional nucleation mechanism. By simulating growth for different values of the bond strengths, we found that both the observed crossover in relative growth rate of the (101) and (110) faces (and resulting habit change) and the double-layer structure of islands on the (110) face arise from a difference in the attachment energy of alternate (110) layers. In contrast, the elongated shape of the islands on (110) is mainly due to the topology of the bonding and is not very dependent on bond strengths.