Functional stability and structural transitions of Kallikrein: spectroscopic and molecular dynamics studies

Multiepitope glycan based laser assisted fluorescent nanocomposite with dual functionality for sensing and ablation of Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) infection is becoming a severe health hazard and needs early diagnosis with high specificity. However, the non-specific binding of a biosensor is a challenge to the current bacterial detection system. For the first time, we chemically synthesized a galactose tripod (GT) as a P. aeruginosa-specific ligand. We conjugated GT to a photothermally active fluorescent nanocomposite (Au@SiO2-TCPP). P. aeruginosa can be detected using Au@SiO2-TCPP-GT, and additionally ablated as well using synergistic photothermal and photodynamic therapy. Molecular dynamics and simulation studies suggested better binding of GT (binding energy = -6.6 kcal mol-1) with P. aeruginosa lectin than that of galactose monopod (GM) (binding energy = -5.9 kcal mol-1). Furthermore, a binding study was extended to target P. aeruginosa, which has a galactose-binding carbohydrate recognition domain receptor. The colorimetric assay confirmed a limit of detection (LOD) of 104 CFU mL-1. We also looked into the photosensitizing property of Au@SiO2-TCPP-GT, which is stimulated by laser light (630 nm) and causes photoablation of bacteria by the formation of singlet oxygen in the surrounding media. The cytocompatibility of Au@SiO2-TCPP-GT was confirmed using cytotoxicity assays on mammalian cell lines. Moreover, Au@SiO2-TCPP-GT also showed non-hemolytic activity. Considering the toxicity analysis and efficacy of the synthesized glycan nanocomposites, these can be utilized for the treatment of P. aeruginosa-infected wounds. Furthermore, the current glycan nanocomposites can be used for bacterial detection and ablation of P. aeruginosa in contaminated food and water samples as well.

Conformational dynamics of superoxide dismutase (SOD1) in osmolytes: a molecular dynamics simulation study

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease caused by the misfolding of Cu, Zn superoxide dismutase (SOD1). Several earlier studies have shown that monomeric apo SOD1 undergoes significant local unfolding dynamics and is the predecessor for aggregation. Here, we have employed atomistic molecular dynamics (MD) simulations to study the structure and dynamics of monomeric apo and holo SOD1 in water, aqueous urea and aqueous urea-TMAO (trimethylamine oxide) solutions. Loop IV (zinc-binding loop) and loop VII (electrostatic loop) of holo SOD1 are considered as functionally important loops as they are responsible for the structural stability of holo SOD1. We found larger local unfolding of loop IV and VII of apo SOD1 as compared to holo SOD1 in water. Urea induced more unfolding in holo SOD1 than apo SOD1, whereas the stabilization of both the form of SOD1 was observed in ternary solution (i.e. water/urea/TMAO solution) but the extent of stabilization was higher in holo SOD1 than apo SOD1. The partially unfolded structures of apo SOD1 in water, urea and holo SOD1 in urea were identified by the exposure of the hydrophobic cores, which are highly dynamic and these may be the initial events of aggregation in SOD1. Our simulation studies support the formation of aggregates by means of the local unfolding of monomeric apo SOD1 as compared to holo SOD1 in water.

Molecular insights into the inhibitory mechanism of bi-functional bis-tryptoline triazole against β-secretase (BACE1) enzyme

The β-site amyloid precursor protein-cleaving enzyme 1 (β-secretase, BACE1) is involved in the formation of amyloid-β (Aβ) peptide that aggregates into soluble oligomers, amyloid fibrils, and plaques responsible for the neurodegeneration in Alzheimer disease (AD). BACE1 is one of the prime therapeutic targets for the design of inhibitors against AD as BACE1 participate in the rate-limiting step in Aβ production. Jiaranaikulwanitch et al. reported bis-tryptoline triazole (BTT) compound as a potent inhibitor against BACE1, Aβ aggregation as well as possessing metal chelation and antioxidant activity. However, the molecular mechanism of BACE1 inhibition by BTT remains unclear. Thus, molecular docking and molecular dynamics (MD) simulations were performed to elucidate the inhibitory mechanism of BTT against BACE1. MD simulations highlight that BTT interact with catalytic aspartic dyad residues (Asp32 and Asp228) and active pocket residues of BACE1. The hydrogen-bond interactions, hydrophobic contacts, and π-π stacking interactions of BTT with flap residues (Val67-Asp77) of BACE1 confine the movement of the flap and help to achieve closed (non-active) conformation. The PCA analysis highlights lower conformational fluctuations for BACE1-BTT complex, which suggests enhanced conformational stability in comparison to apo-BACE1. The results of the present study provide key insights into the underlying inhibitory mechanism of BTT against BACE1 and will be helpful for the rational design of novel inhibitors with enhanced potency against BACE1.

Effect of Osmolytes on Conformational Behavior of Intrinsically Disordered Protein α-Synuclein

α-Synuclein is an intrinsically disordered protein whose function in a healthy brain is poorly understood. It is genetically and neuropathologically linked to Parkinson's disease (PD). PD is manifested after the accumulation of plaques of α-synuclein aggregates in the brain cells. Aggregates of α-synuclein are very toxic and lead to the disruption of cellular homeostasis and neuronal death. α-Synuclein can also contribute to disease propagation as it may exert noxious effects on neighboring cells. Understanding the mechanism of α-synuclein aggregation will facilitate the problem of dealing with neurodegenerative diseases in general and that of PD in particular. Here, we have used molecular dynamics simulations to investigate the behavior of α-synuclein at various temperatures and in different concentrations of urea and trimethyl amine oxide. The residue region from 61 to 95 of α-synuclein is experimentally known as amyloidogenic. In our study, we have identified some other regions, which also have the propensity to form an aggregate besides this known sequence. Urea being a denaturant interacts more with these regions of α-synuclein through hydrogen bond formation and inhibits the β-sheet formation, whereas trimethyl amine oxide itself does not interact much with the protein and stabilizes the protein by preferentially distributing water molecules on the surface of the protein.

Scrutiny of the mechanism of small molecule inhibitor preventing conformational transition of amyloid-β42 monomer: insights from molecular dynamics simulations

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is characterized by loss of intellectual functioning of brain and memory loss. According to amyloid cascade hypothesis, aggregation of amyloid-β₄₂ (Aβ₄₂) peptide can generate toxic oligomers and their accumulation in the brain is responsible for the onset of AD. In spite of carrying out a large number of experimental studies on inhibition of Aβ₄₂ aggregation by small molecules, the detailed inhibitory mechanism remains elusive. In the present study, comparable molecular dynamics (MD) simulations were performed to elucidate the inhibitory mechanism of a sulfonamide inhibitor C1 (2,5-dichloro-N-(4-piperidinophenyl)-3-thiophenesulfonamide), reported for its in vitro and in vivo anti-aggregation activity against Aβ₄₂. MD simulations reveal that C1 stabilizes native α-helix conformation of Aβ₄₂ by interacting with key residues in the central helix region (13-26) with hydrogen bonds and π-π interactions. C1 lowers the solvent-accessible surface area of the central hydrophobic core (CHC), KLVFF (16-20), that confirms burial of hydrophobic residues leading to the dominance of helical conformation in the CHC region. The binding free energy analysis with MM-PBSA demonstrates that Ala2, Phe4, Tyr10, Gln15, Lys16, Leu17, Val18, Phe19, Phe20, Glu22, and Met35 contribute maximum to binding free energy (-43.1 kcal/mol) between C1 and Aβ₄₂ monomer. Overall, MD simulations reveal that C1 inhibits Aβ₄₂ aggregation by stabilizing native helical conformation and inhibiting the formation of aggregation-prone β-sheet conformation. The present results will shed light on the underlying inhibitory mechanism of small molecules that show potential in vitro anti-aggregation activity against Aβ₄₂.