Cell permeating Cupid

PTEN peptide A

B. Cupid-PTEN-A peptide labelled with fluorescein was subjected to SDS-PAGE and observed with a blue light transilluminator.

M = Weight markers shown in Kd

S = Labelled Cupid-PTEN-A peptide sample.

C. Labelled peptide was incubated with living cells at 10 micromolar for 60 minutes before exchanging the media and washing the cells. Cells were imaged using a fluorescence microscope with filter sets for Fluorescein (Upper Panel) or phase contrast (Lower Panel). Fluorescent images of treated cells are taken at a setting where the background (autofluorescence) of the untreated cells is at the threshold of detection. We observe the peptide fluorescence distributed diffusely throughout all cells.

Comment: PTENs mass is actually only 47 kD but it runs as a 55-kilodalton (kD) protein on SDS-PAGE. This difference may be due to the high acidity of part of the protein, slowing its migration on SDS-PAGE, thus making it appear heavier than it actually is (1). The Cupid-PTEN-A peptide contains the acidic region within it which we suggest causes the slightly anomalous migration pattern seen in our laboratory.

(1) Reference.

The anomalous electrophoretic behavior of the human papillomavirus type 16 E7 protein is due to the high content of acidic amino acid residues.

Armstrong DJ, Roman A., Biochem Biophys Res Commun. 1993 May 14;192(3):1380-7.