Insights on the conformation and appropriate drug-target sites on retinal IMPDH1 using the 604-aa isoform lacking the C-terminal extension

Background and purpose: Retinitis pigmentosa (RP) accounts for 2 percent of global cases of blindness. The RP10 form of the disease results from mutations in isoform 1 of inosine 5'-monophosphate dehydrogenase (IMPDH1), the rate-limiting enzyme in the de novo purine nucleotide synthesis pathway. Retinal photoreceptors contain specific isoforms of IMPDH1 characterized by terminal extensions. Considering previously reported significantly varied kinetics among retinal isoforms, the current research aimed to investigate possible structural explanations and suitable functional sites for the pharmaceutical targeting of IMPDH1 in RP. Experimental approach: A recombinant 604-aa IMPDH1 isoform lacking the carboxyl-terminal peptide was produced and underwent proteolytic digestion with α-chymotrypsin. Dimer models of wild type and engineered 604-aa isoform were subjected to molecular dynamics simulation. Findings/Results: The IMPDH1 retinal isoform lacking C-terminal peptide was shown to tend to have more rapid proteolysis (~16% digestion in the first two minutes). Our computational data predicted the potential of the amino-terminal peptide to induce spontaneous inhibition of IMPDH1 by forming a novel helix in a GTP binding site. On the other hand, the C-terminal peptide might block the probable inhibitory role of the N-terminal extension. Conclusion and implications: According to the findings, augmenting IMPDH1 activity by suppressing its filamentation is suggested as a suitable strategy to compensate for its disrupted activity in RP. This needs specific small molecule inhibitors to target the filament assembly interface of the enzyme

In silico studies of anti-oxidative and hot temperament-based phytochemicals as natural inhibitors of SARS-CoV-2 Mpro.

Main protease (Mpro) of SARS-CoV-2 is considered one of the key targets due to its role in viral replication. The use of traditional phytochemicals is an important part of complementary/alternative medicine, which also accompany the concept of temperament, where it has been shown that hot medicines cure cold and cold medicines cure hot, with cold and hot pattern being associated with oxidative and anti-oxidative properties in medicine, respectively. Molecular docking in this study has demonstrated that a number of anti-oxidative and hot temperament-based phytochemicals have high binding affinities to SARS-CoV-2 Mpro, both in the monomeric and dimeric deposited states of the protein. The highest ranking phytochemicals identified in this study included savinin, betulinic acid and curcumin. Complexes of savinin, betulinic acid, curcumin as well as Nirmatrelvir (the only approved inhibitor, used for comparison) bound to SARS-CoV-2 Mpro were further subjected to molecular dynamics simulations. Subsequently, RMSD, RMSF, Rg, number of hydrogen bonds, binding free energies and residue contributions (using MM-PBSA) and buried surface area (BSA), were analysed. The computational results suggested high binding affinities of savinin, betulinic acid and curcumin to both the monomeric and dimeric deposited states of Mpro, while highlighting the lower binding energy of betulinic acid in comparison with savinin and curcumin and even Nirmatrelvir, leading to a greater stability of the betulinic acid-SARS-CoV-2 Mpro complex. Overall, based on the increasing mutation rate in the spike protein and the fact that the SARS-CoV-2 Mpro remains highly conserved, this study provides an insight into the use of phytochemicals against COVID-19 and other coronavirus diseases