Our project!

Paving the way for new diagnostic and therapeutic tools

Our aim is to develop a diagnostic technique based on an artificial, randomly selected and modified peptide. This peptide is capable of detecting the presence of fungal pathogens in a sample collected from a patient. Briefly, our approach is as follows. Through a yeast two-hybrid assay (screening method for protein-peptide interactions) we will select a set of peptides that show affinity towards surface proteins from different fungi (e.g. Aspergillus nidulans, A. fumigatus, Candida albicans or C. glabrata). After confirming the interaction between the surface proteins and a given peptide, we intend to attach a molecule to the peptide marker. In our project, this molecule will be a fluorescent protein, but in principle can also be an immune system activator which is then recognized by the immune cells (macrophages) or other chemical moiety that adds novel functionalities or increases the peptide stability.

Why peptides?

In comparison to antibodies or antibody fragments, synthetic peptides are small (10 to 20 times smaller than an antibody), easily synthesized, modified less expensively and show higher diffusion rates in tissues. We expect that a diagnostic method based on small peptides is more accurate and cheaper than other existing methods and also has the potential for in vivo diagnosis. This could extend the list of existing methods. Furthermore, the adaptability of our approach allows other laboratories to follow it to generate and refine their own peptides with specificity towards their proteins of interest, instead of ordering antibodies. The possibilities of our project is illustrated in figure 1. A large antibody is unable to bind to a protein which is localized in the cell wall (Figure 1A), because of steric hindrance. By contrast, our “PepTag” has, compared to an antibody, the advantage that it is small and thereby can bind to a cell wall protein even if it is masked by other cell wall structures like glycoproteins (Figure 1B).

Figure 1| Schematic comparison of antibody and PepTag in the attempt to bind to a surface molecule. In part A and B from bottom to top of the zoomed-in section, the details are as follow. The Plasma Membrane is on the bottom. On top of it, the cell wall components: the β-1-3 glucan strains in light blue, chitin in purple, the β-1-6 glucan layer in grey, the glycoproteins (like mannoproteins) as red spirals and finally both the plasma membrane proteins and the cell wall proteins can be seen in different shades of green. Part A illustrates an antibody trying to bind, however the presence of the glycoproteins generate a steric impediment for such interaction to occur. Figure B shows how a small peptide attached to a scaffold protein can actually pass in between the glycoproteins and bind successfully to its target cell wall protein. Upon this positive interaction, different applications result evident, in this case the binding of an “Immune System Activator” (e.g. sorts of sugar or a chemical compound) molecule is depicted in orange, which would result in the tagging of a specific fungal strain so as to activate the natural immune system response.

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