Non-ionic surfactants are widely used in protein biosensing technologies to improve sensitivity and specificity. The surfactants inhibit protein aggregation and improve the functionalized surfaces in immunoassays. However, surfactants can potentially act as interfering factors in the assay modifying the protein conformation and the ligand-receptor affinity . In practice, the surfactant concentration in assay buffers is an empirical compromise that is reached without design rules based on molecular understanding. Recently we have developed a torsion profiling technique  based on magnetic particle labels to measure the mechanical properties of individual ligand-receptor pairs. Using a rotating magnetic field, we apply a controlled torque to an individual protein pair sandwiched between a functionalized magnetic particle and a substrate, and thereby determine its torsion constant. The torsion is visualized using fluorescently labelled particles attached to the magnetic bead. In this work, we investigate the interaction of surfactants with the proteinG-IgG molecular complex. The study was conducted at multiple concentrations of the surfactants Tween 20 (nonionic) and SDS (anionic). The data show an increased rotational flexibility of the protein complexes upon addition of both surfactants. Tween 20 is able to decrease the torsion constant of the complex up to a factor of 34 for a concentration 10x above the Critical Micelle Concentration (CMC) whereas SDS induces a factor of 8 decrease at the same concentration. Circular Dichroism (CD) measurements reveal that the secondary structure of the protein G is modified when it interacts with both surfactants, whereas no CD change is observed for the IgG antibody. The underlying interactions of both surfactants with the protein complexes are different and will be discussed. Measuring the torsional rigidity of proteins is a novel method to analyze structural changes of protein complexes at single molecule resolution. The results presented in this paper demonstrate that the mechanical integrity of the protein pair is compromised by surfactants without breaking the ligand-receptor bond.  D. Dorokhin, L. Nieto Garrido, L.J. van IJzendoorn, A.M. de Jong, L. Brunsveld, J. Orsel, M.W.J. Prins, submitted, 2014.  A. van Reenen, F. Gutiérrez-Mejía, L.J. van IJzendoorn, M.W.J. Prins, Biophys. J. 2013, 104, 1073-80.
|Title of host publication||Proceedings of the first European Conference on Novel Technologies for In Vitro Diagnostics, (DIATECH), 6-8 October 2014, Leuven, Belgium|
|Publication status||Published - 2014|
|Event||conference; DiaTech 2014; 2014-10-06; 2014-10-08 - |
Duration: 6 Oct 2014 → 8 Oct 2014
|Conference||conference; DiaTech 2014; 2014-10-06; 2014-10-08|
|Period||6/10/14 → 8/10/14|
Gutierrez Mejia, F. A., IJzendoorn, van, L. J., & Prins, M. W. J. (2014). Altering the torsional rigidity of proteins with surfactants. In Proceedings of the first European Conference on Novel Technologies for In Vitro Diagnostics, (DIATECH), 6-8 October 2014, Leuven, Belgium