C-Npys ( S-3-nitro-2-pyridinesulfenyl) and peptide derivatives can inhibit a serine-thiol proteinase activity from Paracoccidioides brasiliensis

The inhibitory capacity of C-Npys ( S-[3-nitro-2-pyridinesulfenyl]) derivatives over thiol-containing serine proteases has never been tested. In the present work we used an extracellular serine-thiol proteinase activity from the fungal pathogen Paracoccidioides brasiliensis (PbST) to describe a potent inhibitory capacity of Bzl-C(Npys)KRLTL-NH 2 and Bzl-MKRLTLC(Npys)-NH 2. The assays were performed with PbST enriched upon affinity chromatography in a p-aminobenzamidine ( pABA)-Sepharose column. Although PbST can cleave the fluorescence resonance energy transfer peptide Abz-MKRLTL-EDDnp between L–T, the C(Npys) derivatives were not substrates nor were they toxic in a cell detachment assay, allowing therapeutic use. The best inhibitor was Bzl-C(Npys)KRLTL-NH 2 ( K i = 16 nM), suggesting that the peptide sequence promoted a favorable interaction, especially when C(Npys) was placed at a further position from the L–T bond, at the N-terminus. Inhibition was completely reverted with dithioerythritol, indicating that it was due to the reactivity of the C(Npys) moiety with a free SH– group.