Speaker: Prof. Christine Payne
Subject: Material-Cell interactions
Date: 15-10- 2015
Author: Carolien Bastiaanssen
The lab of Christine Payne at Georgia Tech does research to understand how cells interact with materials. Two main focusses of their research are nanoparticle-cell interactions and conducting polymer-cell interactions. Some of the techniques they use are spectroscopy, calorimetry and fluorescence microscopy.
Nanoparticles (NPs) have several important cellular applications. They can be used for imaging, sensing, and nucleic acid or drug delivery. Payne wants to understand how the adsorption of proteins onto the surface of NPs influences their interactions with cells. The layer of proteins around a NP is called the corona. To study the influence of the charge of the NP, cationic and anionic NPs made from polystyrene were mixed with serum (FBS) where the main protein is BSA (net negative charge). The corona proteins were isolated using centrifugation and resuspension in water. After which the supernatant was loaded onto a gel and analysed using electrophoresis. The experiment showed that both cationic and anionic NPs bind BSA.
The images above were obtained with a fluorescence microscope. They show the cells in blue and the NPs in green. The upper two images show the cationic NPs and the lower two images show the anionic NPs. On the left the cells are surrounded by medium (MEM) only and in the right two images the medium also contains BSA. Source: Fleischer and Payne, Nanoparticle-cell interactions: molecular structure of the protein corona and cellular outcomes, Accounts of Chemical Research, 2014 Jul 11
In a next experiment Payne and her colleagues studied the effect of FBS on the biding of NPs to cells. Again they used the cationic and anionic polystyrene NPs. Epi-fluorescence microscopy was used to generate the images. This experiment showed that cationic NPs bind significantly more often to cells when FBS is present than when it is not present. Anionic NPs on the other hand bind significantly more often to cells when FBS is not present. This indicates that cationic NPs with BSA use a different cellular receptor than free BSA, while the anionic NPs with BSA use the same cellular receptor as free BSA. They had a suspicion to which receptors the different NPs bind. To determine whether this is really the case, they looked at competition effects between the NPs and a protein that is known to bind to this specific receptor. When NPs bind to different receptors it suggests that they have different conformations. CD spectroscopy was used to analyse small changes in the secondary structure of the proteins absorbed on the NPs. All these experiments lead to the conclusion that the protein corona structure determines which cell surface receptors are used to bind NPs.
The second part of the talk by Christine Payne was focussed on conducting polymer-cell interactions. The lab of Payne wants to synthesize PEDOT:PSS in cells. PEDOT:PSS are conducting polymers made from PDOT and PSS monomers. Peroxisomes are organelles and they are present in most eukaryotic cells. They contain catalase, a catalyst which is similar to plant enzymes used for the synthesis of PDOT:PSS. Payne and her colleagues deposited the monomers in the peroxisomes and saw that PEDOT:PSS was generated. They repeated this experiment, but now they first boiled the catalase. This caused the enzyme to become denatured and it lost all its enzymatic activity. Yet they still saw that PDOT:PSS was produced. The experiment was done with different proteins as well. One of the proteins they tried was transferrin which transports iron in your blood. This protein was used successful to produce PDOT:PSS. It seems that enzymatic activity is not necessary for the synthesis of PEDOT:PSS, but an iron containing protein is needed. In contrast to the current way of synthesising PEDOT:PSS, this procedure allows you to synthesise this conducting biopolymer in a single step.
I really liked the subject of the seminar by Christine Payne. There were several moments of recognition when something I recently learned in a course was mentioned. Yet there were also parts I could not follow completely.