Crystal Growth Procedure of HIV-1 Protease-Inhibitor KNI-272 Complex for Neutron Structural Analysis at 1.9 Å Resolution

Neutron protein crystallography is advantageous in determining protonation states of target proteins to provide a more precise understanding of the enzymatic mechanism and accurate structure-based drug design. However, a major obstacle is the growth of large protein crystals needed to compensate for the weak flux of the available neutron beam. Here, we report crystal growth of human immunodeficiency virus 1 protease (HIV PR) in a complex with its inhibitor KNI-272 by six different methods. Comparative analysis indicates that top-seeded solution growth (TSSG) and TSSG combined with the floating and stirring technique (TSSG-FAST) are efficient strategies for rapidly obtaining large single crystals and effectively preventing polycrystallization of the seed crystal. Neutron diffraction analysis confirmed that the crystal obtained by TSSG is a high-quality single crystal. Furthermore, crystal shape was observed to be influenced by solution flow, suggesting that the degree of supersaturation significantly affects the crystal growth direction of HIV PR complex. This finding implies that the shape of the HIV PR complex crystal might be controlled by the solution flow rate.