The C-terminal bisphosphorylated proenkephalin-A-(209-237)-peptide from adrenal medullary chromaffin granules possesses antibacterial activity

The chromaffin granules have been shown to be an excellent model to study the processing of proenkephalin-A and chromogranins. Recently, we reported a study dealing with the processing of chromogranin B/secretogranin I and the occurrence of the C-terminal chromogranin B-derived peptide 614–626 which was shown to have antibacterial activity [Strub, J. M., Garcia-Sablone, P., Looning, K., Taupenol, L., Hubert, P., Van Dorsselaer, A., Aunis, D. & Metz-Boutigue, M. H. (1995) Eur. J. Biochem. 229, 356–368], We also observed that this new antibacterial activity present in chromaffin granules was associated with other endogenous protein-derived fragments yet to be characterized. The present study reports the isolation and characterization of a peptide which possesses antibacterial activity and which corresponds to the C-terminal 209–237 sequence of proenkephalin-A. A detailed study using microsequencing and matrix-assisted-laser-desorption time-of-flight mass spectrometry (MALD-TOF MS) allowed us to correlate the antibacterial activity of this peptide named enkelytin (FAEPLPSEEEGESYSKEVPEMEKRYGGFM) with post-translational modifications. Endogenous bisphosphorylated proenkephalin-A-(209–237) was active on Micrococcus luteus and Bacillus megaterium killing bacteria in the 0.2–0.4 μM range but was inactive in similar conditions towards Escherichia coli. Enkelytin shares sequence and structural similarities with the antibacterial C-terminal domain of diazepam-binding inhibitor. According to this similarity, a prediction of secondary structure is proposed for enkelytin and discussed in relation to its biological activity.