Steered molecular dynamics simulations reveal critical residues for (un)binding of substrates, inhibitors and a product to the malarial M1 aminopeptidase

Chemoproteomics validates selective targeting of Plasmodium M1 alanyl aminopeptidase as an antimalarial strategy

New antimalarial drug candidates that act via novel mechanisms are urgently needed to combat malaria drug resistance. Here, we describe the multi-omic chemical validation of Plasmodium M1 alanyl metalloaminopeptidase as an attractive drug target using the selective inhibitor, MIPS2673. MIPS2673 demonstrated potent inhibition of recombinant Plasmodium falciparum (PfA-M1) and Plasmodium vivax (PvA-M1) M1 metalloaminopeptidases, with selectivity over other Plasmodium and human aminopeptidases, and displayed excellent in vitro antimalarial activity with no significant host cytotoxicity. Orthogonal label-free chemoproteomic methods based on thermal stability and limited proteolysis of whole parasite lysates revealed that MIPS2673 solely targets PfA-M1 in parasites, with limited proteolysis also enabling estimation of the binding site on PfA-M1 to within ~5 Å of that determined by X-ray crystallography. Finally, functional investigation by untargeted metabolomics demonstrated that MIPS2673 inhibits the key role of PfA-M1 in haemoglobin digestion. Combined, our unbiased multi-omic target deconvolution methods confirmed the on-target activity of MIPS2673, and validated selective inhibition of M1 alanyl metalloaminopeptidase as a promising antimalarial strategy.

Chemoproteomics validates selective targeting of Plasmodium M1 alanyl aminopeptidase as an antimalarial strategy

New antimalarial drug candidates that act via novel mechanisms are urgently needed to combat malaria drug resistance. Here, we describe the multi-omic chemical validation of Plasmodium M1 alanyl metalloaminopeptidase as an attractive drug target using the selective inhibitor, MIPS2673. MIPS2673 demonstrated potent inhibition of recombinant Plasmodium falciparum ( Pf A-M1) and Plasmodium vivax ( Pv A-M1) M1 metalloaminopeptidases, with selectivity over other Plasmodium and human aminopeptidases, and displayed excellent in vitro antimalarial activity with no significant host cytotoxicity. Orthogonal label-free chemoproteomic methods based on thermal stability and limited proteolysis of whole parasite lysates revealed that MIPS2673 solely targets Pf A-M1 in parasites, with limited proteolysis also enabling estimation of the binding site on Pf A-M1 to within ~5 Å of that determined by X-ray crystallography. Finally, functional investigation by untargeted metabolomics demonstrated that MIPS2673 inhibits the key role of Pf A-M1 in haemoglobin digestion. Combined, our unbiased multi-omic target deconvolution methods confirmed the on-target activity of MIPS2673, and validated selective inhibition of M1 alanyl metalloaminopeptidase as a promising antimalarial strategy.

Role of salt-bridging interactions in recognition of viral RNA by arginine-rich peptides

Interactions between RNA molecules and proteins are critical to many cellular processes and are implicated in various diseases. The RNA-peptide complexes are good model systems to probe the recognition mechanism of RNA by proteins. In this work, we report studies on the binding-unbinding process of a helical peptide from a viral RNA element using nonequilibrium molecular dynamics simulations. We explored the existence of various dissociation pathways with distinct free-energy profiles that reveal metastable states and distinct barriers to peptide dissociation. We also report the free-energy differences for each of the four pathways to be 96.47 ± 12.63, 96.1 ± 10.95, 91.83 ± 9.81, and 92 ± 11.32 kcal/mol. Based on the free-energy analysis, we further propose the preferred pathway and the mechanism of peptide dissociation. The preferred pathway is characterized by the formation of sequential hydrogen-bonding and salt-bridging interactions between several key arginine amino acids and the viral RNA nucleotides. Specifically, we identified one arginine amino acid (R8) of the peptide to play a significant role in the recognition mechanism of the peptide by the viral RNA molecule.

Biochemical and cellular characterisation of the Plasmodium falciparum M1 alanyl aminopeptidase (PfM1AAP) and M17 leucyl aminopeptidase (PfM17LAP)

The Plasmodium falciparum M1 alanyl aminopeptidase and M17 leucyl aminopeptidase, PfM1AAP and PfM17LAP, are potential targets for novel anti-malarial drug development. Inhibitors of these aminopeptidases have been shown to kill malaria parasites in culture and reduce parasite growth in murine models. The two enzymes may function in the terminal stages of haemoglobin digestion, providing free amino acids for protein synthesis by the rapidly growing intra-erythrocytic parasites. Here we have performed a comparative cellular and biochemical characterisation of the two enzymes. Cell fractionation and immunolocalisation studies reveal that both enzymes are associated with the soluble cytosolic fraction of the parasite, with no evidence that they are present within other compartments, such as the digestive vacuole (DV). Enzyme kinetic studies show that the optimal pH of both enzymes is in the neutral range (pH 7.0-8.0), although PfM1AAP also possesses some activity (< 20%) at the lower pH range of 5.0-5.5. The data supports the proposal that PfM1AAP and PfM17LAP function in the cytoplasm of the parasite, likely in the degradation of haemoglobin-derived peptides generated in the DV and transported to the cytosol.

Random acceleration and steered molecular dynamics simulations reveal the (un)binding tunnels in adenosine deaminase and critical residues in tunnels

Adenosine deaminase (ADA) is an important enzyme related to purine nucleoside metabolism in human serum and various tissues. Abnormal ADA levels are related to a wide variety of diseases such as rheumatoid arthritis, AIDS, anemia, lymphoma, and leukemia and ADA is considered as a useful target for various diseases. Currently, ADA can be divided into open conformation and closed conformation according to the inhibitors of binding. As a consequence, we chose two inhibitors, namely, 6-hydroxy-1,6-dihydro purine nucleoside (PRH) and N-[4,5-bis(4-hydroxyphenyl)-1,3-thiazol-2-yl]hexanamide (FRK) to bind to ADA in the closed conformation or open conformation respectively. In this study, we performed the random acceleration molecular dynamics (RAMD) method, steered molecular dynamics (SMD) simulations and adaptive basing force (ABF) simulation to explore the unbinding tunnels and tunnel characteristics of the two inhibitors in ADA. Our results showed that PRH and FRK escaped from ADA using three main tunnels (namely, T1, T2, and T3). Inhibitors (PRH and FRK) escape through T3 more frequently and more easily. The results from ABF simulations confirm that the free energy barrier in T1 or T2 is larger than that in T3 when inhibitors dissociate from the ADA and have potential mean of force (PMF) depth. Moreover, in the complexes (ADA-PRH, ADA-FRK), we also found that the most active residue that remarkably contributed to the binding affinity is W117 in T3, and the residue played an important role in the unbinding tunnel for inhibitor leaving. Our theoretical study provided insight into the ADA inhibitor passway mechanism and may be a clue for potent ADA inhibitor design.

Molecular dynamics simulations provide molecular insights into the role of HLA-B51 in Behçet's disease pathogenesis

Behçet's disease is an inflammatory disorder of unknown etiology. Genetic tendency has an important role in its pathogenesis, and HLA-B51, a class I MHC antigen, has been recognized as the strongest susceptibility factor for Behçet's disease. Despite the confirmation of the association of HLA-B51 with Behçet's disease in different populations, its pathogenic mechanisms remain elusive. HLA-B51 differs in only two amino acids from HLA-B52, other split antigen of HLA-B5, which is not associated with Behçet's disease. These two amino acids are located in the B pocket of the antigen-binding groove, which occupies the second amino acids of the bound peptides. To understand the nature of the HLA-peptide interactions, differences in structure and dynamics of two HLA alleles were investigated by molecular dynamics simulations using YAYDGKDYI, LPRSTVINI, and IPYQDLPHL peptides. For HLA-B51, all bound peptides fluctuated to larger extent than HLA-B52. Free energy profiles of unbinding process for YAYDGKDYI by steered molecular dynamics simulations showed that unbinding from HLA-B52 results in greater free energy differences than HLA-B51. These results suggest the possibility of an instability of HLA-B51 associated with the repertoire of peptides, and this finding may provide significant insight to its pathogenic role in Behçet's disease.