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  • The binding of TQ to

    2023-12-06

    The binding of TQ to hsALDH changes the characteristic (-)-Bicuculline methobromide mg spectrum of the enzyme. Therefore, TQ forms a complex with hsALDH and changes its absorption properties [39]. Ksv and Kb values indicate that the binding of TQ to hsALDH is very strong and of the order of static binding (complex formation). There is approximately a 1:1 binding ratio of TQ and hsALDH [40]. Far-UV CD analysis showed that there was no significant change in the secondary structure of hsALDH upon binding to TQ. Also, the effect of temperature on the binding between the two showed that the binding constant decreases with increase in temperature. This further indicates that the quenching of fluorescence by TQ is static and there is a formation of complex between TQ and hsALDH. With increase in temperature, the hsALDH-TQ complex destabilizes and therefore binding constant decreases due to gain in molecular kinetic energy and increase in Brownian motion [41], [42]. However, the decrease in binding constant (-)-Bicuculline methobromide mg was from 2.34±0.07×105M−1 to 1.00±0.09×105M−1 when the temperature was increased from 15°C to 37°C. The binding constant is still of the order of 105 at 37°C, which is strong enough to show its activating effect. Therefore, at physiological temperature (37°C), TQ strongly binds to hsALDH and hence will activate the enzyme to a good extent. Protein-ligand interaction primarily involves the non-covalent interactions such as hydrogen bonding, electrostatic interactions, hydrophobic interactions and Van der Waals forces [43], [44]. TQ contains three methyl groups on its surface along with two ring carbonyl groups. The methyl groups along with the aromatic ring provide the hydrophobic and van der Waals forces for binding to the enzyme. Also, partial negative charge on the carbonyl oxygen may contribute to the binding through hydrogen bond formation and electrostatic interaction. A negative ΔH and a positive ΔS value (Table 4) shows that the electrostatic interactions are also involved in the hsALDH-TQ complex formation. The free energy of binding (ΔG value, Table 4) shows that there is strong binding between TQ and hsALDH resulting in complex formation. Also, negative value of ΔG (-1.26×104Jmol−1) shows that the binding of TQ to hsALDH is a spontaneous process. FRET analysis shows that the emission spectrum of hsALDH and the absorption spectrum of TQ overlap with an r value of 4.16nm and therefore, energy transfer could take place between hsALDH and TQ. Also, it was found that 0.5Roacid residues. Being an anti-oxidant, TQ is very much likely to ensure that the catalytic cysteine residue remains in the reduced form for catalysis. TQ binds to the active site close to the catalytic cysteine residue. The kinetic analysis depicted that it influences both the dehydrogenase and esterase activity of the enzyme, both of which involve a common catalytic cysteine residue. Binding of TQ leads to the lowering of the Km value of the enzyme, implying that it increases the affinity of the enzyme for the substrate. The increase in the Vmax value shows that it also favours the catalytic activity of the enzyme. Docking analysis revealed that TQ fits into the active site near the catalytic cysteine residue through multiple non-covalent interactions with some of the highly conserved amino acid residues. Also, TQ enhances the substrate binding affinity and catalytic efficiency without altering the secondary structure of the enzyme. This is likely possible if TQ binds to the active site, close to the substrate binding site and in close proximity with the catalytic cysteine residue. TQ, under in vivo conditions, shows antioxidant, anticancer, cytoprotective property, etc. through a number of mechanisms [26], [46]. It protects the activity of antioxidant enzymes in vivo[23], [34]. It also maintains the oral health [31]. HsALDH which is mainly ALDH3A1 is an antioxidant enzyme involved in the detoxification of aldehydes and maintenance of oral health [6]. It is expressed in the epithelial cells of upper aero-digestive tract (UADT) including oral cavity, larynx, pharynx and esophagus [47]. Activity of the enzyme is important for protection of individuals from cancer of UADT including oral cancer [6], and reduced level of this enzyme make individuals vulnerable to cancer and other aldehyde related pathogenesis in the UADT [8]. The activation of hsALDH and perhaps ALDHs in general by TQ may be one of the possible mechanism through which it shows some of these pharmacological properties in vivo. Increased activity of ALDH has many health benefits in normal individuals [17]. Activation of the enzyme by a natural molecule is a potential pharmacological chaperone therapy against aldehyde related pathogenesis. The overview and general significance of the study is schematically represented in Fig. 13.