Investigating hydrogen peroxide induced damage to alpha-2-macroglobulin: Biophysical and thermodynamic study

Insight into the molecular interaction between the anticancer drug, enzalutamide and human alpha-2-macroglobulin: Biochemical and biophysical approach

The drug pharmacokinetics is affected upon binding with proteins, thus making drug-protein interactions crucial. This study investigated the interaction between enzalutamide and human major antiproteinase alpha-2-macroglobulin (α2M) by using multi spectroscopic and calorimetric techniques. The spectroscopic techniques such as circular dichroism (CD), intrinsic fluorescence, and UV-visible absorption were used to determine the mechanism of enzalutamide-α2M interaction. Studies on the quenching of fluorescence at three different temperatures showed that the enzalutamide-α2M complex is formed through static quenching mechanism. The change in microenvironment around tyrosine residues in protein was detected through synchronised fluorescence. The secondary structure of α2M was slightly altered by enzalutamide according to far UV-CD spectral analysis. Changes in position of amide I band in FTIR spectra further confirm the secondary structural alteration in α2M. According to thermodynamic characteristics such as fluorescence quenching and isothermal titration calorimetry (ITC), hydrogen bonds and hydrophobic interactions were involved in the interaction machanism. The ITC reiterated the exothermic and spontaneous nature of the interaction. The lower proteinase inhibitory activity of the α2M-enzalutamide conjugate as reflects the disruption of the native α2M structure upon interaction with enzalutamide.

Comprehensive insight into the molecular interaction of an anticancer drug-ifosfamide with human alpha-2-macroglobulin: biophysical and in silico studies

Ifosfamide is an active alkylating chemotherapeutic drug chemically related to nitrogen mustard. The pharmacokinetics of drugs is affected upon binding with protein, making the studies on drug-protein interaction promising. The present study investigates the interaction between ifosfamide and human antiproteinase-alpha-2-macroglobulin (α₂M) by using multi-spectroscopic and in silico techniques. The UV-visible absorption, intrinsic fluorescence and circular dichroism (CD) spectroscopic methods were employed to unveil the mode and mechanism of ifosfamide-α₂M interaction. Fluorescence quenching studies performed at three different temperatures indicated that ifosfamide-α₂M complex formation involves static quenching. Far UV-CD spectra revealed a minor alteration in the secondary structure of α₂M instigated by ifosfamide. The thermodynamic parameters determined by fluorescence quenching experiment and isothermal titration calorimetry (ITC) suggested that the complex between ifosfamide and α₂M involves hydrogen bonding and hydrophobic interactions. Molecular docking illustrates that ifosfamide binds with moderate affinity to Lys1240, Asn173, Ser957, Leu955, Asp953, Lys1216 and Thr1236 residues during the interaction. Molecular dynamic (MD) simulation suggested that the ifosfamide forms a stable complex with α₂M. Communicated by Ramaswamy H. Sarma.

Characterization of the binding between anti-tumor drug 5-fluorouracil and human alpha-2-macroglobulin: spectroscopic and molecular docking analyses

5-Fluorouracil (5-FU) is a well-recognized anticancer drug used in the treatment of tumors of head, neck and breast. Drug pharmacokinetics is affected upon binding with protein, thus, making drug-protein interactions imperative to study. Present work investigates the interaction between 5-FU and human major antiproteinase-alpha-2-macroglobulin (α₂M) by multi-spectroscopic, calorimetric and molecular docking techniques. UV/Visible absorption, intrinsic fluorescence and circular dichroism (CD) spectroscopic methods have been employed to unveil the mode and mechanism of 5-FU-α₂M interaction. Synchronous fluorescence showed alteration in the microenvironment of tryptophan and tyrosine residues of protein. Far UV-CD spectra suggest slight alterations in the secondary structure of α₂M by 5-FU. Thermodynamic parameters determined by fluorescence quenching experiments and isothermal titration calorimetry (ITC) suggested the involvement of hydrogen bonds and hydrophobic interactions. Moreover, ITC corroborate the spontaneous and exothermic nature of the interaction process. Molecular docking illustrates that 5-FU binds with moderate affinity and Asp953, Tyr1264, Lys1236, Thr1232, Tyr1323 and Leu951 were the main residues involved. Molecular dynamics simulation studies suggested that 5-FU was stabilizing the α₂M structure and forming a stable complex. It was concluded that 5-FU lower the antiproteolytic activity of α₂M significantly and causes disruption in the native structure and conformation of α₂M.Communicated by Ramaswamy H. Sarma.

Quercetin-induced inactivation and conformational alterations of alpha-2-macroglobulin: multi-spectroscopic and calorimetric study

Quercetin is a widely used bioflavonoid found in onions, grapes, berries and citrus fruits. Under certain conditions, quercetin acts as a pro-oxidant thereby generating reactive oxygen species and promoting the oxidation of molecules. Our study investigates the effect of quercetin on the structure and function of alpha-2-macroglobulin (α₂M) by employing various biophysical techniques and trypsin inhibitory assay. α₂M is the major antiproteinase present in the plasma of vertebrates. Results of activity assay indicated that α₂M loses its 56% of inhibitory activity on treatment with quercetin in the presence of light. UV spectroscopy reveals hyper chromaticity in absorption spectra of protein on interaction with quercetin suggesting structural change. The intrinsic fluorescence studies showed quenching of α₂M spectra in the presence of quercetin, and the mode of quenching was found to be static in nature. Synchronous fluorescence indicated the alteration in the microenvironment of tryptophan residues. CD and FTIR spectroscopy confirms concentration-dependent alterations in secondary structure of α₂M instigated by quercetin. The magnitude of binding constant, enthalpy change, entropy change and free energy change during the interaction process was determined by isothermal titration calorimetry. Hydrogen bonding and hydrophobic interaction were the main intermolecular forces involved during the process. This study identifies and signifies the damage induced by quercetin to α₂M due to its pro-oxidant action. Communicated by Ramaswamy H. Sarma.