Md Simulation
The MD was carried out from the docking between the flavonoids that presented the best score and the gp63 proteins (apo form) of L. major and with a simulation time of 500 ns. The RMSD, RMSF, Radius of gyration, and Solvent Accessible Surface Area (SASA) among other values were used to evaluate the stability of apo-protein and protein-ligand complexes.
The mean square deviation (RMSD) of the Cα atoms concerning the movements of their initial position was used to determine the stability of the complexes formed by the four biflavonoids amentoflavone (A), lanaroflavone (L), podocarpusflavone A (PA), and podocarpusflavone B (PB) with the leishmanolysin (gp63) (Fig S1) from L. major. The RMSD data of the protein, the ligand-protein, and the ligand alone are shown in Fig. 1. The complexes 1LML-A, 1LML-L, 1LML-PA, and 1LML-PB, follow a similar trend to the apo-1LML form (1.66 ± 0.21 Å), with RMSD values of 2.28 ± 0.27 Å, 1.79 ± 0.13 Å, 2.04 ± 0.14 Å, and 2.30 ± 0.16 Å, respectively. All proteins and complexes converge after 20 to 80 ns, indicating that all simulated systems of L. major reach stability at 500 ns simulation.
To look at the positional stability of the compounds, the RMSD of each of the biflavonoids was determined in the pocket of the 1LML protein (Fig. 2), during the 500 ns trajectory the fluctuations are kept below 2 Å. The average values in the 1LML for ligand were 1.55 ± 0.21 Å, 2.25 ± 0.36 Å, 1.43 ± 0.20 Å and 2.17 ± 0.60 Å, for A, L, PA, and PB respectively. Principally, the four biflavonoids reach their convergence in the protein studied, although certain fluctuations will depend on the protein-ligand complex.
The RMSF was calculated to reveal the differences in the fluctuation of the local regions for the two systems. The RMSF for the biflavonoids A (black), L (purple), PA (orange), and PB (green) in complex with the proteins 1LML (blue) has been calculated from the Cα shown in Fig. 3. In the case of biflabonoids, show fluctuations in the RMSF values in the complex 1LML-A regions comprising residues 125–143, and 218–252. The complex formed by 1LML-PA presents the greatest fluctuations between amino acids 320–336, while in 1LML-PB the fluctuations are little, the most relevant being residues 317–335 and 490–505. There are a few variations for the 1LML-L complex that show the conformational position of each of the molecules under study at different times of the simulation, where it is observed most of the time, that they remained in the binding sites of the 1LML during the simulation.
Radius Of Gyration (Rg) Analysis
The compactness measure was calculated to determine possible changes in the folding and conformation of the structure of the proteins under study. The mean radius of gyration for 1LML is 2.34 ± 0.10 nm, 2.35 ± 0.18 nm, 2.34 ± 0.29 nm, 2.33 ± 0.01 nm, and 2.34 ± 0.38 nm, for the 1LML, 1LML-A, 1LML- L, 1LML-PA, and 1LML-PB, respectively, Fig. S2. Based on the average values observed, biflavonoids produce compact and stable complexes compared to apo-1LML.
Solvent Accessible Area (Sasa)
All protein-biflavonoid complexes show a low SASA score when compared with the apo form of L. major leishmanolysin, the tendency is to maintain up to 500 ns of the simulation, achieving its stability, Fig. S3. The SASA values of 204.89 ± 2.31 nm2, 209.63 ± 2.98 nm2, 206.00 ± 2.64 nm2, 207.54 ± 2.37 nm2, and 205.29 ± 2.24 nm2 for apo-1LML, 1LML-A, 1LML-L, 1LML-PA, and 1LML-PB, respectively.
H-bonds Analysis
The docking carried out for the biflavonoids reveals the particular interactions are hydrophobic, H-bonds, metal-contact, and π-stacking (π-π T-shaped). The MD simulation reveals the number of hydrogen bonds during the trajectory for the four biflavonoids studied. In the 1LML, a small number of conformations exhibited between 1 and more than 7 H-bonds (Fig. 4). Amentoflavone, lanaroflavone, and podocarpusflavones A and B form an average of 2.0, 3.0, 2.0, and 1.0 with the 1LML, respectively. Among the amino acid residues at the end of the simulated 100 ns form H-bond between leismanoliysin and the biflavonoids, Gly222, Val223, Leu224, Ala225, His264, Glu265, Ala346, Ala350, Ser421, Ser462, and Ser465 stand out. The biflavonoids form hydrogen bonds that stabilize the complex during the simulation. Being the lanoroflavone that best stabilizes the structure of the 1LML protein.
Principal component analysis
A dynamic cross-correlation matrix (DCCM) was generated to identify correlated or anti-correlated movements with the L. major gp63 protein bound to the studied biflavonoids. Figure 5 shows the DCCM maps for the protein gp63 alone and the gp63 in complexes with ligands.
The correlation ranges from − 1 to 1, corresponding to the degree of correlation or anti-correlation as indicated by the respective color intensities. The color cyano represents positive correlation values in the range between 0.25 and 1. Magenta color represents negative correlation values ranging from − 0.25 to − 1; and the colors cyano light or light magenta represent a weak or no correlation, for values between − 0.25 and + 0.25. The cyano, and magenta comparing the regions for 1LML alone and 1LML-PB show anti-correlation movements (blue box), being more intense in the complex. In a similar region the other complexes show a negative but less intense correlation compared to 1LML alone and the 1LML-PB complex, in the 1LML-A, 1LML-L, and 1LML-PA complexes the same areas compared to the protein native anti-correlation movements are minor. On the other hand, a positive correlation (red boxes) is present in all systems, being less intense in the 1LML-PB complex.
Movement changes between the residues in the proteins are observed, when the complexes and the apo-proteins are compared, suggesting that ligand interaction affects the movements in the residues. A Principal Component Analysis (PCA) through an MD simulation initially reveals the changes in motion during the trajectory of the protein. This is performed by calculating the eigenvectors (Total movement of the atoms) and the eigenvalues (atomic contribution for each movement) to better understand the structural and conformational changes of the gp63 due to the presence of the ligands.
To investigate and analyze the effect of biflavonoids on the conformational states of 1LML protein in an in-phase principal component (PC) space, PCA analysis was performed for all Cα atoms in the protein of L.major gp63 and their complexes with the biflavonoids in the 500 ns of the trajectory, respectively. The PCA was commonly used to reduce the dimensionality of MD simulation data and identify conformational transformations.
To highlight the differences in the collective movement of the 1LML protein in the system studied. In theory, the first three principal components (PC1, PC2, and PC3) of PCA capture most of the variance in the original distribution of conformational sets in molecules. The CA indicated that the first three PCs represented 22.6%, 50.2%, 46.7%, 39.5%, and 31.3% in the movement variance observed in the trajectories of apo-1LML, 1LML-A, 1LML-L, 1LML-PA, and 1LML-PB, respectively. The 1LML-A, had the highest value followed by the 1LML-L, while the 1LML-PB was the lowest even than the 1LML alone, Fig. S4. The simulated conformations in each system were dynamic and fluctuated during the 500 ns MD simulations, eventually stabilizing in a dominant state. The conformational changes between the 1LML protein with or without ligand were different, aligning with their respective structures (Fig. 6).
The RMSD, RMSF, Rg, and SASA values were stable throughout the MD simulation for the two proteins. Slight differences in these values occur between 1LML when they interact with biflavonoids. The H-bond number for each protein, 1LML, varies slightly when this parameter is compared, with lanaroflavone that shows the highest values at the end of the 500 ns simulation H-bonds for both proteins. The PCA carried out shows the conformational changes produced by the interaction between the biflavonoids and the 1LML protein. Each value is associated with an eigenvalue that reflects the direction of movement and the corresponding magnitudes of fluctuation. The first 20 PCA reflect 60% for 1LML, showing that the three eigenvectors were representative of the fluctuation between atoms in the conformational changes for the two proteins interacting with the tested ligands.
Binding energy estimation
In silico drug, design has been an active area of research in recent years (Kumari et al. 2014). Virtual screening, docking, molecular dynamics, as well as MMPBSA free energy calculation of compounds have been widely used in recent years for the design of new drugs (Jürgen Bajorath. 2022). This study was based on the interaction between biflavonoids and the Leishmanolisin (gp63) proteins of L. major, a metalloprotease that belongs to class M8 (subclan MA (M), metzincins) (Russo et al. 2020). The free energy of binding of the complexes in the active site for the leismanolysin protein of L. major was calculated according to the MMPBSA method. To estimate the binding of the ligands with the proteins along the trajectory of the 500 ns simulation, the calculation of the free binding energy of these compounds was determined whose values are summarized in Table 1. The ΔGbind for amentoflavone (-163.39 ± 60.09 Kcal/mol), lanaroflavone (-156.75 ± 31.91 Kcal mol), podocarpuflavone A and B (-134.20 ± 33.26 Kcal/mol and − 112.06 ± 36.23 Kcal/mol, respectively). The negative values of the van der Waals contribution for each ligand are highlighted, being the lowest value for lanaroflavone (-226.80 ± 31.91) and the highest for podocarpusflavone B (-203.94 ± 40.33), in comparison with the electrostatic interaction energies, the latter being higher, evidenced by the low formation of hydrogen bridges as should be expected for these polyhydroxylated compounds.
Table 1
Summary of protein–compound binding energies according to MMPBSA
Ligand
|
van der Waals energy
|
Electrostatics
energy
|
Polar
solvation
energy
|
SASA
energy
|
Binding
energy
|
Amentoflavone
|
-199.88 ± 43.24
|
-49.14 ± 22.91
|
105.18 ± 31.18
|
-19.55 ± 5.62
|
-163.39 ± 60.09
|
Lanaroflavone
|
-226.80 ± 31.91
|
-72.39 ± 18.29
|
164.23 ± 41.98
|
-21.79 ± 3.56
|
-156.75 ± 31.91
|
Podocarpusflavone A
|
-215.69 ± 22.44
|
-83.79 ± 51.76
|
178.26 ± 36.05
|
-12.98 ± 1.26
|
-134.20 ± 33.26
|
Podocarpusflavone B
|
-203.94 ± 40.33
|
-42.45 ± 14.69
|
146.31 ± 19.02
|
-11.98 ± 2.37
|
-112.06 ± 36.23
|
All values are in Kcal mol− 1 |
Important differences between the 1LML protein and the complexes formed with the ligands under study were observed. The analysis of the contribution of residues to the binding energy for each complex is crucial for the stabilization of complex protein-biflavonoids. The contribution per-residues are shown in Fig. 7 for each 1LML-biflavonois complex, it can be observed the most favorable residues in the interaction such as Leu224, Asp255, and Leu257. On the other hand, for the 1LML-Lanoroflavone complex, the active site residues His264, Glu265, and His334 are unfavorable to the interaction with the ligand, on the contrary case for the other bioflavonoids where these same residues are favored in their interaction with the protein.
Further, the time scale was calculated for each biflavonoids in complex with leihsmanolysin protein. The Overlap for 0 ns, 100 ns, 250 ns, and 500 ns are shown in Fig. 8, lanaroflavone moved away from the active site amino acids of the protein at the end of the simulation (green color, 500 ns). In the case of the other compounds, the orientation they take at the end of the simulation is very similar.
Physicochemical, pharmacokinetic, and toxicity properties
The analysis of pharmacokinetic characteristics (ADME) reveals that all four compounds violate drug-likeness in terms of molecular weight and logP (Table S1), according to the analysis performed in SwissADME, taking into consideration physical and pharmacokinetic properties. It can be observed that the studied biflavonoids present high logP values above the stipulated values. As for the pharmacokinetic values, the molecules studied show low GI absorption and none is permeable to the blood-brain barrier penetration (BBB), which contrasts with the poor solubility of the four compounds, in addition to not being good substrates for the P-gp protein. As for lanaroflavone and podocarpusflavone A, both exhibit inhibition of metabolism by CYP2C9 liver enzymes, while amentoflavone and podocarpusfalvone B do not exhibit inhibition of any of the metabolizing enzymes.
The toxicity of the biflavonoids was predicted using the ProTox-II platform. The LD50 predicted for the four molecules was high according to the toxicity scale of the program, which was higher than 7.27 mM Kg− 1. Hepatoxicity, immunotoxicity, carcinogenicity, and cytotoxicity were evaluated, being all inactive except for podocarpusflavone A and B which presented a high probability of immunotoxicity.
Numerous publications have presented biflavonoids as potential antiprotozoal candidates. Thus, lanaroflavone Weniger et al. have reported that this biflavonoid shows moderate antiplasmodial activity in vitro. The same author reports that lanroflavone has activity on L. donovani amastigotes of IC50 3.9 µg/mL (Wenige et al. 2020). In the case of amentoflavone, activity has been reported for this compound which was active against L. amazonenis amastigotes in murine macrophages. In this case, an IC50 of 2.3 ± 0.93 µM is reported, reducing total amastigotes by 57%. It also reduced lesions in a subcutaneous treatment at 21 days compared to the control group (Silva et al. 2020). On the other hand, the biflavonoids podocarpusflavone A and B showed little activity on the promastigote of L. donovani (Del Rayo et al. 2000).
In this in silico study, they reveal that naturally occurring biflavonoid compounds such as amentoflavone, lanaroflavone, podocarpusflavone A, and B can bind to the 1LML, inhibiting them of these, and therefore possibly preventing the entrance of the promastigote into the host.