The effect of sarafloxacin on Cu/ZnSOD structure and activity Zhaozhen Cao a,b , Rutao Liu a,⇑ , Ziliang Dong c , Xinping Yang a , Yadong Chen d a School of Environmental Science and Engineering, China–America CRC for Environment & Health, Shandong University, 27# Shanda South Road, Jinan 250100, Shandong Province, PR China b School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, Shandong Province, PR China c China Research Institute of Daily Chemical Industry, Taiyuan 030001, Shanxi Province, PR China d Laboratory of Molecular Design and Drug Discovery, School of Basic Science, China Pharmaceutical University, Nanjing 210009, PR China highlights  The effects of sarafloxacin on Cu/ ZnSOD structure and activity were investigated.  Sarafloxacin can bind to Cu/ZnSOD mainly through hydrogen bond and hydrophobic forces.  The binding process tends to be saturated as the concentration of sarafloxacin reaches 4 times of Cu/ ZnSOD.  The binding induces structure change in Cu/ZnSOD but does not affect its activity.  Sarafloxacin binds to the surface of b- barrel of Cu/ZnSOD far away from the active site and active site channels. graphical abstract The effects of sarafloxacin on Cu/ZnSOD were evaluated via investigating the structure and the structure basis activity changes of Cu/ZnSOD upon sarafloxacin binding using multi-spectroscopic methods, iso- thermal titration microcalorimetry (ITC) and molecular docking method. Sarafloxacin binds to a hydro- phobic area located on the surface of b-barrel and tends to form hydrogen bonds with Tyr 108, Pro 100, Asp 25 and Ser 103 residues around it. The binding of sarafloxacin induces structure change in Cu/ZnSOD but does not affect its activity, which can be attributed to the active site and active site channel of Cu/ZnSOD being far away from the binding site and the microenvironment of them not to be affected. article info Article history: Received 16 July 2014 Received in revised form 30 August 2014 Accepted 18 September 2014 Available online 13 October 2014 Keywords: Cu/ZnSOD Sarafloxacin Multi-spectroscopic methods ITC Molecular docking Enzyme activity abstract The effect of sarafloxacin to Cu/ZnSOD was evaluated via investigating the change in Cu/ZnSOD structure and the structure basis activity upon sarafloxacin binding. Multi-spectroscopic methods, isothermal titration microcalorimetry (ITC) and molecular docking method were adopted in this study. Sarafloxacin binds to Cu/ZnSOD mainly through hydrophobic and hydrogen bond forces and tends to be saturated as the molar ratio of sarafloxacin to Cu/ZnSOD reaches 4. The binding changed the microenvironment around Tyr and the secondary structure of Cu/ZnSOD but did not affect the activity of Cu/ZnSOD. Molec- ular docking study revealed that sarafloxacin binds into a hydrophobic area with possibility to form hydrogen bonds with Tyr 108, Asp 25, Pro 100 and Ser 103 of Cu/ZnSOD. The binding area locates on the surface of b-barrel close to the second Greek key loop (GK2) and V-loop but far away from the active site and active site channel of Cu/ZnSOD. These promoted the understanding of the experiment phenom- enons. The binding of sarafloxacin does not affect the activity of Cu/ZnSOD should attribute to the binding not to change the microenvironment of Cu/ZnSOD active site and active site channel. Ó 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2014.09.073 1386-1425/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel./fax: +86 531 88364868. E-mail address: rutaoliu@sdu.edu.cn (R. Liu). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 136 (2015) 601–606 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa