Identification of substrate-analog trypsin inhibitors through the screening of synthetic peptide combinatorial libraries.

Synthetic peptide combinatorial libraries (SPCLs), which are made up in total of tens to hundreds of millions of peptides, enable the systematic screening for biologically active peptides in virtually all in vitro and even in vivo assay systems. In the current study, the applicability of this method to the identification of peptide enzyme inhibitors was investigated using trypsin as the model enzyme. A specifically designed library of hexapeptide mixtures was synthesized on cotton carriers and screened. The synthetic approach, using cotton as a solid support, was modified so that the deprotected peptides remained attached to the cotton carrier until they were released into solution directly prior to being assayed. Following an iterative process of synthesis and screening, in which all of the positions of the sequence were successively defined, a number of individual hexapeptides with trypsin inhibitory activity were identified. The most active, defined individual peptide sequence was then reincorporated into a new library, now made up of dodecapeptide mixtures. The iterative screening and synthesis of this library led to a dodecapeptide with improved inhibitory activity when compared to the hexapeptide from which it was derived.