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The human formyl peptide receptor 2 (FPR2) is a G-protein coupled receptor which is physiologically expressed on immune cell lineages like neutrophils and T-cells. Among other peptides the FPR2 senses the Staphylococcus aureus toxin PSMα3. It was suggested by Cheung et al 2014 that the binding mechanism relies on the formylated N-terminus of the peptide as well as on the C-terminus. In response to receptor activation FPR2 elicits a signaling cascade depending on calcium ions as second messengers. Ultimately this leads to immune cell activation, secretion of inflammatory cytokines and chemotaxis. All of this is connected with an inflammatory outcome in vivo. The neutrophil activation by FPR2 is therefore an important mechanism of its toxicity because it leads to an aggravation of the inflammation related symptoms in Staphylococcus aureus infection.

This Biobrick can be used in signaling studies or the cellular detection of several small formylated amyloidogenic peptides. As a controls two peptides with inhibitory (WRWW4) and activating (WKYMVm) effect on FPR2 are available.

To investigate the FPR2 receptor we generated a eGFP-tagged FPR2 fusion construct for transfection of HEK293 cells. This construct was designed with an C-terminal HA-tag to be used for antibody staining and GFP for analyzing the cellular localization of FPR2 via microscopy. Transfected HEK293 cells were analyzed by flow cytometry using mouse anti-Human FPR2 coupled to Alexa647 antibody to detect membrane localization of FPR2 (Fig.1)

Knowing that FPR2-eGFP is expressed on the surface of HEK293 cells, we proceeded with calcium influx assays of those cells using our chemically synthesized L-PSMα3. Treating HEK293_FPR2-eGFP cells with 700nM L-PSMα3 an increase in intracellular calcium release was detected (Fig. 2A). Although this was relatively low compared to the ionomycin control, no change in calcium flux was detected in non-transfected HEK293 cells (Fig. 3). The membrane location and specific activation of FPR2 was moreover tested by adding the potent peptide activator WKYMVm (REF) to HEK293_FPR2-eGFP cells (Fig. 2B).