RESEARCH ARTICLE The binding interaction between cadmium‐based, aqueous‐phase quantum dots with Candida rugosa lipase Lining Zhao 1 | Shimeng Hu 1 | Qiwei Meng 1 | Mengchen Xu 1 | Hao Zhang 2 | Rutao Liu 1 1 School of Environmental Science and Engineering, Shandong University, China‐ America CRC for Environment & Health, Shandong Province, Jinan, P. R. China 2 Laboratory of Immunology for Environment and Health, Shandong Analysis and Test Center, Qilu University of Technology (Shandong Academy of Sciences), Jinan, China Correspondence Rutao Liu, School of Environmental Science and Engineering, Shandong University, Jinan, Shandong Province, P.R. China. Email: rutaoliu@sdu.edu.cn Hao Zhang, Laboratory of Immunology for Environment and Health, Shandong Analysis and Test Center, Qilu University of Technology (Shandong Academy of Sciences), Jinan, China. Email: zhanghao0911@yeah.net Funding information Ministry of Education of China, Grant/Award Numbers: 20130131110016 and 708058; NSFC, Grant/Award Numbers: 21777088, 21477067 and 21277081; Natural Science Foundation of Shandong Province, Grant/ Award Number: ZR2016YL013; Science and Technology Development Plan of Shandong Province, Grant/Award Number: 2014GSF117027; Research Fund for the Doctoral Program of Higher Education; Culti- vation Fund of the Key Scientific and Technical Innovation Project Abstract As a promising biolabeling biomaterials, quantum dots (QDs) present a great potential. However, the toxicity of QDs to organisms has attracted wide attention. In our research, we introduced an in vitro method to study the molecular mechanisms for the structure and activity alterations of Candida rugosa lipase (CRL) with the binding of 3‐mercaptopropionic acid‐capped CdTe QDs. Multiple spectroscopic methods, isothermal titration calorimetry, and enzyme activity measure- ments were used in this paper. QDs statically quenched the intrinsic fluorescence of CRL with the quenching constant decreases from 2.46 × 10 13 to 1.64 × 10 13 L mol -1 second -1 (298 to 310 K). It binds to CRL through hydrophobic force with 1 binding site, unfolding and loosening the skeleton and changed its secondary structure. Rather than aggregating on the surface, it enters the pocket of the CRL to interact with Ser‐209 (2.43 Å) and the residues surrounding Ser‐209, making the catalytic triad more exposed. Furthermore, the activity of CRL was inhibited by approximately 15%. This work demonstrates that 3‐mercaptopropionic acid‐capped CdTe QDs may cause negative effects to CRL and obtains a molecular mechanism on QD‐induced toxicity to proteins in vitro. KEYWORDS calorimetry, Candida rugosa lipase, MPA‐capped CdTe QDs, spectroscopy, toxicity 1 | INTRODUCTION Quantum dots (QDs) possess the highly photoluminescent property, and thus, they have great advantages for the application in the fields of chemistry, electronics, medicine and biological labeling/imaging, and biocatalysis. 1-6 To date, many methods have been used for the synthesis of QDs with high photoluminescence quantum yield during the past 2 decades. 7-10 To improve biocompatibility, hydrophobic QDs need to be transferred from the organic phase to aqueous solution. 11 In this paper, the aqueous‐phase QDs we used were synthesized as described in our previous study. 12 As a cadmium nano- particle, CdTe QDs can liberate cadmium and accumulate in the organs and tissues and, thus, affect cell growth and viability. 13-16 Many conditions (size, shape, surface coating, and so on) influence the toxic- ity of QDs to living organizms. 17,18 The uptake of xenobiotics potentially affects the protein function. In our previous work, CdTe QDs are found to influence the structure of many biomacromolecules, which lead to effect on their activity. 19 By investigating the molecular mechanism of the xenobiotics' effect on pro- teins, we would understand better how proteins are affected. 20 Studying the interaction of CdTe QDs with proteins would be of great value and potential to reveal the mechanism of cadmium and nanoparticle toxicity. Serine proteases function in many biological systems to hydrolyze specific polypeptide bonds. They have the triad of residues Ser‐Asp‐ His at the active site. Studies suggest that they may serve as a functional interacting unit responsible for bond formation and cleavage Received: 28 December 2017 Revised: 24 January 2018 Accepted: 18 February 2018 DOI: 10.1002/jmr.2712 J Mol Recognit. 2018;e2712. https://doi.org/10.1002/jmr.2712 Copyright © 2018 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/jmr 1 of 9