The Pattern Recognition And Mechanism Researches Of Human TLR8 Agonists

Toll Like Receptors(TLRs)are important pattern recognition receptors(PRRs)in the human immune system,which can recognize pathogen-associated molecular patterns(PAMPs)and activate human innate immune responses.As the receptor of single stranded RNA(ssRNA),hTLR8(Human Toll Like Receptor 8)is closely related to the treatment of tumors,microbial infections and inflammatory diseases.Therefore,the studies on pattern recognition and mechanism of hTLR8 agonists have important theoretical and practical values for the development of immunomodulatory drugs.In this paper,emerging chemical pattern(ECP)and molecular docking methods were firstly utilized to molecular recognition studies of hTLR8 agonists.Furthermore,molecular dynamics(MD)and targeted molecular dynamics(TMD)simulations were applied to explore the conformational changes and signal transduction processes during hTLR8 activation.In general,this work can provide valuable references for the development of hTLR8 agonists and mechanism researches.The main results and conclusions are summarized as follows:(1)ECP was utilized to predict the key chemical patterns of 97 hTLR8 agonists from 114 non-gonists.Based on the ECPs discovered,a robust and predictive ECP model with only 6 descriptors was derived with the prediction accuracies of 83.3%,81.0%,and 80.0% for 132 training samples,79 validation samples,and 75 test samples,respectively.When applying the ECP model with molecular docking method,the hit rate of TLR8 agonists was greatly enhanced.Based on the results of ECP-based hierarchical cluster analysis and connolly surface analysis of TLR8 receptor,the results showed that H-bond,hydrophilic and hydrophobic potentials as well as the unbalanced degree in property distributions are very important for distinguishing the TLR8 agonists from non-agonists.(2)ECP was utilized to discriminat the key chemical patterns of 97 hTLR8 agonists and 29 antagonists.An optimal ECP model using only 3 descriptors was established with prediction accuracies of 93.4% and 92.2% for 76 training samples and 50 test samples,respectively.The results showed that H-bonded is the most important feature for discrimination of hTLR8 agonists and antagonists.(3)Based on the hTLR8 crystal structure,the ligand-unbound(apo)state of hTLR8 were constructed after homology modeling and kinetic optimization.The three co-crystallized agonists,i.e.,CL097,CL075 and R848,were docked to hTLR8 apo state by using Surflex-Dock procedure.The results show that the stable transition state models were formed by CL097,CL075 and R848-hTLR8 complexs.H-bonding,electrostatic and hydrophobic interactions widely exist in agonists and hTLR8 binding pocket.(4)With the transition state models and the holo states as the initial and the targeted conformations,TMD simulation method were applied to explore the conformational changes and signal transduction of hTLR8 activation.Acoording to the analysis of RMSF and H-bond interactions,it is speculated that the hTLR8 conformational changes induced by agonists are conducted via the hydrogen-bond interaction mediated by the outer layer of the LRR,especially the charged amino acid residues.The activation signal is generated at the binding site and transmitted from the proximal to distal ends,eventually triggering the dimerization of the hTLR8 monomers.