A positive-charged patch and stabilized hydrophobic core are essential for avirulence function of AvrPib in the rice blast fungus.

Fungal avirulence effectors, a key weapon utilized by pathogens to promote their infection, are recognized by immune receptors to boost host R gene-mediated resistance. Many avirulence effectors share sparse sequence homology to proteins with known functions, and their molecular and biochemical functions together with the evolutionary relationship among different members remain largely unknown. Here, the crystal structure of AvrPib, an avirulence effector from Magnaporthe oryzae, was determined and showed a high degree of similarity to the M. oryzae Avrs and ToxB (MAX) effectors. Compared with other MAX effectors, AvrPib has a distinct positive-charge patch formed by five positive-charged residues (K29, K30, R50, K52 and K70) on the surface. These five key residues were essential to avirulence function of AvrPib and affected its nuclear localization into host cells. Moreover, residues V39 and V58, which locate in the hydrophobic core of the structure, cause loss of function of AvrPib by single-point mutation in natural isolates. In comparison with the wild-type AvrPib, the V39A or V58A mutations resulted in a partial or entire loss of secondary structure elements. Taken together, our results suggest that differences in the surface charge distribution of avirulence proteins could be one of the major bases for the variation in effector-receptor specificity, and that destabilization of the hydrophobic core is one of the major mechanisms employed by AvrPib for the fungus to evade recognition by resistance factors in the host cell.

Structural optimization of pyrrolopyrimidine BTK inhibitors based on molecular simulation.

CONTEXT: BTK is a critical regulator involved in the proliferation, differentiation, and apoptosis of B cells. BTK inhibitors can effectively alleviate various diseases such as tumors, leukemia, and asthma. During this study, a range of novel BTK inhibitors were designed using 3D-QSAR, molecular docking, and molecular dynamics (MD) simulation. METHODS: We selected 41 pyrrolopyrimidine derivatives as BTK inhibitors to structure a 3D-QSAR model. Comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA) were adopted to research the connection between the pharmacological activities and chemical structures of the compounds. The CoMFA model (q2 = 0.519, R2 = 0.971), CoMSIA model (q2 = 0.512, R2 = 0.990), and external validation demonstrated excellent predictive performance and reliability of the 3D-QSAR model. We designed eight novel molecules with higher inhibitory activities according to the three-dimensional equipotential fields and explored the interactions between the compounds and BTK by molecular docking, which showed that the novel molecules had higher binding affinities with BTK than the template molecule 18. Then, the results of molecular docking were further verified by MD simulation, which showed that amino acid residues such as Leu528, Val416, and Met477 played vital parts in the interaction, and the binding free energy analysis showed that the novel molecules had higher stability with BTK. Finally, the ADME/T properties were predicted for all of the novel compounds, and the results showed that the majority of them had favorable pharmacokinetic properties. Therefore, this study provides strong support for the development of novel BTK inhibitors.