Adsorption of lysozyme on pH-responsive PnBA-b-PAA polymeric nanoparticles: studies by stopped-flow SAXS and ITC
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The interactions of poly(n-butyl acrylate)-b-poly(acrylic acid) (PnBA-b-PAA) block copolymer nanoparticles with lysozyme were examined by a stopped-flow technique consisting of small-angle X-ray scattering (SAXS) and isothermal titration calorimetry (ITC). Nanoparticles composed of PnBA-b-PAA block copolymer had a spherical shape and core-shell structure, which was confirmed by cryo-transmission electron microscopy (cryo-TEM) and SAXS. ITC revealed that lysozyme binds to the nanoparticle surface and that the strength of the binding depends on the ionic strength of the solution and the composition of the PnBA-b-PAA copolymers. Thermodynamic results unambiguously indicated that the interaction of lysozyme with the nanoparticle surface is a two-step process and entropy driven. Stopped-flow experiments proved that lysozyme penetration into the PAA corona occurs on a time scale of hundreds of milliseconds. Based on the fitting of SAXS curves, the number of micelles per volume increases with time, the core size remains nearly constant, and the thickness of the shell decreases. Such findings justify the model proposed in our previous papers.
KeywordsPolymeric nanoparticles Lysozyme Small-angle X-ray scattering Stopped-flow Cryo-TEM Isothermal titration calorimetry
We thank EMBL and DESY for allocating beam time and providing excellent equipment. The authors acknowledge Lubomir Kovacik and Sami Kereiche for the cryo-TEM measurements.
We acknowledge financial support from the Ministry of Education, Youth and Sports of the Czech Republic, grant no. LH15213.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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