Exploring a potential allosteric inhibition mechanism in the motor domain of human Eg-5

Kinesin-5 (Eg-5), microtubule motor protein, is one of the emerging drug targets in cancer research. Several inhibitors have been reported to bind the hEg-5 “motor domain” in two different locations that are potentially allosteric. Interestingly, the crystal structure of Eg-5 bound to benzimidazole unveils two chemically different allosteric pockets (PDB ID: 3ZCW). The allosteric modulators inhibit Eg-5 activity by causing conformational changes that affect nucleotide turnover rate. In the present work, three allosteric inhibitors were simulated along with the substrate nucleotides (ADP and ATP) to capture conformation changes induced by the allosteric inhibitors. To analyze the allosteric inhibition mechanism, we used dynamics cross-correlation, principal component analysis (PCA), and enthalpic calculations. The loop L5 interaction is determined by the type of substrate bind at the nucleotide binding site. The SW-II flexibility increased upon dual allosteric inhibition by SB-743921 and 6a. The ionic interaction between R221-E116 is observed only in the presence of two allosteric inhibitors. Also, we noticed that the α2/α3 helical orientation is responsible for the SW-1 loop position and substrate binding. Our simulation data suggest the critical chemical features required to block the motor domain by the allosteric inhibitors. The results summarized in this work will help the researchers to design better therapeutic agents targeting hEg-5.

Communicated by Ramaswamy H. Sarma