| The interaction study plays a leading role in screening and designing veterinary drugs with high efficiency.The interactions of several antimicrobial veterinary drugs with serum albumins and DNA were inestigated by multi-spectroscopy and molecular docking.The interaction between sulfaclozine sodium monohydrate/marbofloxacin and bovine serum albumin（BSA）/human serum albumin（HSA）were studied by spectroscopy and molecular docking.The two drugs statically quenched the fluorescence of serum albumins with non-radiative energy transfer.The binding constants（Ka）and the number of binding sites（n）were obtained(291 K,p H=7.40,sulfaclozine sodium monohydrate-BSA:Ka=4.85×10~4 L·mol–1,n=1.06,r0=1.88nm;marbofloxacin-BSA:Ka=1.66×10~4 L·mol–1,n=0.99;sulfaclozine sodium monohydrate-HSA:Ka=9.45×10~4 L·mol–1,n=1.24;marbofloxacin-HSA:Ka=9.70×10~3 L·mol–1,n=0.94).Based on F（?）rster non-radiative energy transfer（FRET）theory,the binding distances（r0）of sulfaclozine sodium monohydrate with BSA and HSA were 3.32 nm and 3.11 nm respectively;the r0of marbofloxacin with BSA and HSA were 4.28 nm and 3.34 nm respectively.The analysis of thermodynamic parameters showed that sulfaclozine sodium monohydrate bound spontaneously to serum albumins mainly through electrostatic attraction and marbofloxacin bound to serum albumins mainly through hydrogen bond and van der Waals force.The circular dichroism（CD）spectroscopy and Fourier Transform infrared（FT-IR）spectroscopy revealed that the two drugs changed the secondary structure of serum albumins.Sulfaclozine sodium monohydrate and marbofloxacin bound at Sub-domain IIA of serum albumins.The interaction between monensin/clopidol and BSA/HSA were studied by spectroscopy and molecular docking.Fluorescence spectra and fluorescence lifetime analysis showed that the fluorescence quenching of serum albumins by the two drugs were static quenching.The values of Ka,n and r0 were obtained(291 K,p H=7.40,monensin-BSA:Ka=5.42×10~4 L·mol–1,n=1.23,r0=1.88 nm;clopidol-BSA:Ka=4.96×10~4 L·mol–1,n=1.16,r0=2.53 nm;monensin-HSA:Ka=3.22×10~4 L·mol–1,n=1.01,r0=2.19 nm;clopidol-HSA:Ka=2.99×10~4 L·mol–1,n=1.00,r0=2.02nm).Both monensin and clopidol bound spontaneously to serum albumins mainly by hydrogen bond and van der Waals force.Monensin and clopidol bound to serum albumins at Sub-domain IIA and changed the secondary structures of serum albumins.The molecular docking results were consistent with the spectral results.The interaction between florfenicol and DNA was studied by spectroscopy,viscosity,melting temperature,ionic strength,single and double stranded DNA comparison approaches and molecular docking.Viscosity analysis showed that the viscosity of DNA hardly changed with increasing florfenicol.The melting temperature between DNA and florfenicol-DNA was almost no difference.Ionic strength way showed that the fluorescence intensity of the florfenicol with DNA system decreased with the increase of Na Cl content.The single and double stranded DNA comparison method showed that the value of Ka for florfenicol with single stranded DNA（ss DNA）(3.57×10~3·L·mol–1)was less than the value of Ka for florfenicol with double stranded DNA（ds DNA）(6.92×10~3·L·mol–1).The CD spectra analysis showed that the addition of florfenicol reduced the base stacking degree and increased the helicity of DNA.The FT-IR spectroscopy showed that florfenicol caused the changes in the secondary structure of DNA.The ultraviolet-visible（UV-vis）spectra analysis showed that DNA had hyperchromic effect on florfenicol.Above results revealed that florfenicol bound to DNA through groove binding mode.The results from molecular docking further showed that flofenicol bound to the groove of DNA.Fluorescence spectra and fluorescence lifetime analysis showed that DNA statically quenched the fluorescence of florfenicol.The values of Ka for florfenicol-DNA were 6.92×10~3 L·mol–1,6.21×10~3 L·mol–1 and 5.61×10~3 L·mol–1at 291 K,301 K and 311 K respectively.Electrostatic attraction was the dominant force of the interaction.The interaction between tiamulin and DNA was studied by multi-spectroscopy and molecular docking.The CD spectra revealed the base stack force became stronger and the right-hand helicity became looser for DNA due to the addition of tiamulin.The viscosity,melting temperature,ionic strength,single and double stranded DNA comparison and molecular docking methods all showed that tiamulin was inserted into DNA.The fluorescence quenching of tiamulin by DNA was static quenching.The values of Ka were 8.13×10~3 L·mol–1,6.31×10~3 L·mol–1 and 4.90×10~3 L·mol–1 at 291 K,301 K and 311 K respectively from fluorescence method;the value of Ka was 9.51×10~3 L·mol–1 at 291 K from ultraviolet method. |
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