Computer simulation as a tool for tracing the conformational differences between proteins in solution and in the crystalline state.

Knowledge about the architecture of macromolecules has been derived primarily from crystallography. Therefore, it has been a matter of concern whether the conformation of a macromolecule in solution, namely in vivo, might be different from that in the crystalline state. To determine the difference between the conformations, a protein (trypsin inhibitor) dissolved in water has been simulated using the method of molecular dynamics and the results are compared with those obtained from a simulation of the full crystalline unit cell. We report here that no significant difference was found for backbone atoms, except for two more or less flexible loops extending from the core of the protein and the very flexible carboxyterminal residues. The side-chains in which the conformation in solution differs considerably from that in the crystal all belong to polar residues.