A Survey of Prohormone Convertase 2 (PC2) Substrate Specificity Using Substrate Phage Display and Combinatorial Chemistry

Abstract

The substrate and inhibitory specificity of PC2, a mammalian enzyme involved in the cleavage of many constitutively expressed protein precursors, was studied using substrate phage display and combinatorial chemistry. In the method of substrate phage display, a multitude of substrate sequences are displayed as fusion proteins on filamentous phage particles. The cleaved phage are propagated and submitted to additional rounds of protease selection to further enrich for good substrates. DNA sequencing of the cleaved phage is used to identify the preferred substrate sequences. To modify substrate phage display technique using a low pH enzyme the method was optimized for elution with a low pH buffer. After 6 rounds of sorting a substrate phage library containing S random amino acids (XXXXX) there was no consensus sequence among the eluted phage. Combinatorial· chemistry using a positional scanning synthetic combinational library (PS-SCL) offers a unique and rapid approach for the identification of individual active compounds from libraries made up of millions of compounds. The PS-SCL described here is made up of six individual positional peptide libraries, each one consisting of hexamers with a single position defined and five positions as mixtures. The PS-SCL aided in the identification of two inhibitory sequences for PC2. The first is Ac-IIRVKR-NH2 with an ICSO value of 13 µM and the second is Ac-IKRVKR-NH2 with an 1C50 value of 36 µM. These two sequences show the recognition sequence for PC2 to be possibly -RVKR-. While PC2 and PC 1 are in the same family and are both neuroendocrine processing enzymes they do not share similar inhibitory or simulatory poly-amino acid sequences. Modifications of the substrate phage display method for selection with a low pH enzyme are still required. The inhibitory sequence found through using a PS-SCL further aids in understanding the specificity and active site of the enzyme PC2.