Role of the conserved water molecules in the binding of inhibitor to IMPDH-II (human): A study on the water mimic inhibitor design

Halogen Bonding on Water─A Drop in the Ocean?

Halogen bonding is a valuable interaction in drug design, offering an unconventional way to influence affinity and selectivity by leveraging the halogen atoms' ability to form directional bonds. The present study evaluates halogen-water interactions within protein binding sites, demonstrating that targeting a water molecule via halogen bonding can in specific cases contribute beneficially to ligand binding. In solving and examining the crystal structure of 2-cyclopentyl-7-iodo-1H-indole-3-carbonitrile bound to DYRK1a kinase, we identified a notable iodine-water interaction, where water accepts a halogen bond with good geometric and energetic features. This starting point triggered further investigations into the prevalence of such interactions across various halogen-bearing ligands (chlorine, bromine, iodine) in the PDB. Using QM calculations (MP2/TZVPP), we highlight the versatility and potential benefits of such halogen-water interactions, particularly when the water molecule is a stable part of the binding site's structured environment. While the interaction energies with water are lower compared to other typical halogen bond acceptors, we deem this different binding strength essential for reducing desolvation costs. We suggest that "interstitial" water molecules, as stable parts of the binding site engaging in multiple strong interactions, could be prime targets for halogen bonding. Further systematic studies, combining high-resolution crystal structures and quantum chemistry, are required to scrutinize whether halogen bonding on water is more than a "drop in the ocean".

Dynamics of nucleoplasm in human leukemia cells: A thrust towards designing anti-leukemic agents

The human inosine monophosphate dehydrogenase (hIMPDH) is a metabolic enzyme that possesses a unique ability to self-assemble into higher-order structures, forming cytoophidia. The hIMPDH II isoform is more active in chronic myeloid leukemia (CML) cancer cells, making it a promising target for anti-leukemic therapy. However, the structural details and molecular mechanisms of the dynamics of hIMPDHcytoophidia assembly in vitro need to be better understood, and it is crucial to reconstitute the computational nucleoplasm model with cytophilic-like polymers in vitro to characterize their structure and function. Finally, a computational model and its dynamics of the nucleoplasm for CML cells have been proposed in this short review. This research on nucleoplasm aims to aid the scientific community's understanding of how metabolic enzymes like hIMPDH function in cancer and normal cells. However, validating and justifying the computational results from modeling and simulation with experimental data is essential. The new insights gained from this research could explain the structure/topology, geometrical, and electronic consequences of hIMPDH inhibitors on leukemic and normal cells. They could lead to further advancements in the knowledge of nucleoplasmic chemical reaction dynamics.

Bionics design of affinity peptide inhibitors for SARS-CoV-2 RBD to block SARS-CoV-2 RBD-ACE2 interactions

Coronavirus Disease 2019 (COVID-19), has already posed serious threats and impacts on the health of the population and the country's economy. Therefore, it is of great theoretical significance and practical application value to better understand the process of COVID-19 infection and develop effective therapeutic drugs. It is known that the receptor-binding structural domain (SARS-CoV-2 RBD) on the spike protein of the novel coronavirus directly mediates its interaction with the host receptor angiotensin-converting enzyme 2 (ACE2), and thus blocking SARS-CoV-2 RBD-ACE2 interaction is capable of inhibiting SARS-CoV-2 infection. Firstly, the interaction mechanism between SARS-CoV-2RBD-ACE2 was explored using molecular dynamics simulation (MD) coupled with molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) free energy calculation method. The results of energy analysis showed that the key residues R403, R408, K417, and Y505 of SARS-CoV-2 RBD and the key residues D30, E37, D38, and Y41 of ACE2 were identified. Therefore, according to the hotspot residues of ACE2 and their distribution, a short peptide library of high-affinity SARS-CoV-2 RBD was constructed. And by using molecular docking virtual screening, six short peptides including DDFEDY, DEFEDY, DEYEDY, DFVEDY, DFHEDY, and DSFEDY with high affinity for SARS-CoV-2 RBD were identified. The results of MD simulation further confirmed that DDFEDY, DEYEDY, and DFVEDY are expected to be effective inhibitors. Finally, the allergenicity, toxicity and solubility properties of the three peptide inhibitors were validated.

New biochemical insights into the dynamics of water molecules at the GMP or IMP binding site of human GMPR enzyme: A molecular dynamics study

Human GMP reductase (hGMPR) enzyme is involved in a cellular metabolic pathway, converting GMP into IMP, and also it is an important target for anti-leukemic agents. Present computational investigations explain dynamical behavior of water molecules during the conformational transition process from GMP to IMP using molecular dynamics simulations. Residues at substrate-binding site of cancerous protein (PDB Id. 2C6Q) are mostly more dynamic in nature than the normal protein (PDB Id. 2BLE). Nineteen conserved water molecules are identified at the GMP/IMP binding site and are classified as (i) conserved stable dynamic and (ii) infrequent dynamic. Water molecules W11, W14, and W16 are classified as conserved stable dynamic due to their immobile character, whereas remaining water molecules (W1, W2, W3, W4, W5, W7, W8, W9, W10, W12, W13, W15, W17, W18, and W19) are infrequent with dynamic nature. Entrance or displacement of these infrequent water molecules at GMP/IMP sites may occur due to forward and backward movement of reference residues involving ligands. Four water molecules of hGMPR-I and nine water molecules of hGMPR-II are observed in repetitive transitions from GMP to IMP pathway, which indicates discrimination between two isoforms of hGMPRs. Water molecules in cancerous protein are more dynamic and unstable compared to normal protein. These water molecules execute rare dynamical events at GMP binding site and could assist in detailed understanding of conformational transitions that influence the hGMPR's biological functionality. The present study should be of interest to the experimental community engaged in leukemia research and drug discovery for CML cancer.

Investigation of structural analogs of hydroxychloroquine for SARS-CoV-2 main protease (Mpro): A computational drug discovery study

The main protease (Mpro) is the key enzyme of nCOVID-19 and plays a decisive role that makes it an attractive drug target. Multiple analysis of crystal structures reveals the presence of W1, W2, and W3 water locations in the active site pocket of Mpro; W1 and W2 are unstable and are weakly bonded with protein in comparison to W3 of Mpro-native. So, we adopt the water displacement method to occupy W1 or W2 sites by triggering HCQ or its analogs to inactivate the enzyme. Virtual screening is employed to find out best analogs of HCQ, molecular docking is used for water displacement from catalytic region of Mpro, and finally, MD simulations are conducted for validation of these findings. The docking study reveals that W1 and W2 are occupied by respective atoms of ZINC28706440 whereas W2 by HCQ and indacaterol. Finally, MD results demonstrate (i) HCQ occupies W1 and W2 positions, but its analogs (indacaterol and ZINC28706440) are inadequate to retain either W1 or W2 (ii) His41 and Asp187 are stabilized by W3 in Mpro-native and His41, Cys145 and HCQ by W7 in ZINC28706440, and W4, W5, and W6 make water mediated bridge between indacaterol with His41. The structural, dynamical, and thermodynamic (WFP and J value) profiling parameters suggest that W3, W4, and W7 are prominent in their corresponding positions in comparison with W5 and W6. The final results conclude that ZINC28706440 may act as a best analog of HCQ with acceptable physico-chemical and toxicological scores and may further be synthesized for experimental validation.

Structural and Dynamical Impact of Water Molecules at Substrate- or Product-Binding Sites in Human GMPR Enzyme: A Study by Molecular Dynamics Simulations

Human guanosine monophosphate reductase (hGMPR) enzyme maintains the intracellular balance between adenine and guanine nucleotide pools, and it is an excellent target for the design of isoform-specific antileukemic agents. In the present study, we have investigated solvation properties of substrate GMP or product inosine-5'-monophosphate (IMP)-binding pocket of hGMPR by employing molecular dynamics simulations on conformations A (substrate GMP), B [substrate GMP with cofactor nicotinamide adenine dinucleotide phosphate (NDP)], C (product IMP with cofactor NDP), and D (product IMP). Nineteen water sites are identified precisely; they are responsible for the catalytic activity of this site, control structural and dynamical integrity, and electronic consequences of GMP or IMP in the binding site of hGMPR. The water sites of category-1 (W1, W4, W5, W6, W13, and W15) in normal protein and category-2 (W2, W3, W7, W8, W10, W17, and W18) in cancerous protein are unique and stabilize the guanosine or inosine group of GMP or IMP for participation in the enzymatic reaction, whereas the remaining water centers either stabilize pentose sugar ribose or the phosphate group of GMP or IMP. Furthermore, water sites of category-4 (W11, W14, and W16) appear to be conserved in all conformations during the entire simulation. The GMP-binding site in cancerous protein 2C6Q is significantly expanded, and its dynamics are very different from normal protein 2BLE. Furthermore, unique interactions of GMP(N1)···W2···Asp129/Asn158, IMP(N1)···W3···Glu289, and IMP(O6)···W10···Ser270 might be used in a water mimic drug design for hGMPR-II. In this context, water finding probability, relative interaction energy (J) associated with water site W, entropy, and topologies of these three water sites are thermodynamically acceptable for the water displacement method by the modified ligand. Hence, their positions in the catalytic pocket may also facilitate future drug discovery for chronic myelogenous leukemia by the design of appropriately oriented chemical groups that may displace these water molecules to mimic their structural, electronic, and thermodynamic properties.

Conserved water-mediated recognition and dynamics of NAD+ (carboxamide group) to hIMPDH enzyme: water mimic approach toward the design of isoform-selective inhibitor

Inosine monophosphate dehydrogenase (IMPDH) enzyme involves in GMP biosynthesis pathway. Type I hIMPDH is expressed at lower levels in all cells, whereas type II is especially observed in acute myelogenous leukemia, chronic myelogenous leukemia cancer cells, and 10 ns simulation of the IMP-NAD(+) complex structures (PDB ID. 1B3O and 1JCN) have revealed the presence of a few conserved hydrophilic centers near carboxamide group of NAD(+). Three conserved water molecules (W1, W, and W1') in di-nucleotide binding pocket of enzyme have played a significant role in the recognition of carboxamide group (of NAD(+)) to D274 and H93 residues. Based on H-bonding interaction of conserved hydrophilic (water molecular) centers within IMP-NAD(+)-enzyme complexes and their recognition to NAD(+), some covalent modification at carboxamide group of di-nucleotide (NAD(+)) has been made by substituting the -CONH2group by -CONHNH2 (carboxyl hydrazide group) using water mimic inhibitor design protocol. The modeled structure of modified ligand may, though, be useful for the development of antileukemic agent or it could be act as better inhibitor for hIMPDH-II.

Improved estimation of protein-ligand binding free energy by using the ligand-entropy and mobility of water molecules

We previously developed the direct interaction approximation (DIA) method to estimate the protein-ligand binding free energy (DG). The DIA method estimates the DG value based on the direct van der Waals and electrostatic interaction energies between the protein and the ligand. In the current study, the effect of the entropy of the ligand was introduced with protein dynamic properties by molecular dynamics simulations, and the interaction between each residue of the protein and the ligand was also weighted considering the hydration of each residue. The molecular dynamics simulation of the apo target protein gave the hydration effect of each residue, under the assumption that the residues, which strongly bind the water molecules, are important in the protein-ligand binding. These two effects improved the reliability of the DIA method. In fact, the parameters used in the DIA became independent of the target protein. The averaged error of DG estimation was 1.3 kcal/mol and the correlation coefficient between the experimental DG value and the calculated DG value was 0.75.

Role of salt bridge dynamics in inter domain recognition of human IMPDH isoforms: an insight to inhibitor topology for isoform-II

Inosine monophosphate dehydrogenase (IMPDH) enzyme involves in the biosynthesis pathway of guanosine nucleotide. Type II isoform of the enzyme is selectively upregulated in neoplastic fast replicating lymphocytes and CML cancer cells. The hIMPDH-II is an excellent target for antileukemic agent. The detailed investigation during MD-Simulation (15 ns) of three different unliganded structures (1B3O, 1JCN and 1JR1) have clearly explored the salt bridge mediated stabilization of inter or intra domain (catalytic domains I(N), I(C) with res. Id. 28-111 and 233-504, whereas two CBS domains C₁, C₂ are 112-171 and 172-232) in IMPDH enzyme which are mostly inaccessible in their X-rays structures. The salt bridge interaction in I(N)---C₁ inter-domain of hIMPDH-I, I(N)---C₂ of IMPDH-II and C₁---I(C) of nhIMPDH-II are discriminative features among the isoforms. The I(N)---C₂ recognition in hIMPDH-II (1B3O) is missing in type-I isoform (1JCN). The salt bridge interaction D232---K238 at the surface of protein and the involvement of three conserved water molecules or the hydrophilic centers (WA²³²(OD1), WB ²³²(OD2) and W²³⁸(NZ)) to those acidic and basic residues seem to be unique in hIMPDH-II. The hydrophilic susceptibility, geometrical and electronic consequences of this salt bridge interaction could be useful to design the topology of specific inhibitor for hIMPDH-II which may not be effective for hIMPDH-I. Possibly, the aliphatic ligand containing carboxyl, amide or hydrophilic groups with flexible structure may be implicated for hIMPDH-II inhibitor design using the conserved water mimic drug design protocol.