Development, Synthesis and Applications of Highly Sensitive Fluorescent Probes for Studying Protein Tyrosine Phosphatases

Protein tyrosine phosphatases (PTPs) constitute an important class of enzymes that are involved in various cellular processes such as mitogenesis, cell growth, signal transduction, immune response and gene transcription. PTP targeted therapeutics have been slow to develop in part, because the substrate selectivity of the PTPs is not well understood and also due to unavailability of suitable probes to study PTP selectivity. Herein is described the design and synthesis of highly fluorescent probes that provide a highly sensitive, continuous assay for PTP activity and are readily incorporated into peptide substrates for high-throughput screening or activity-based assays. These probes are efficiently hydrolyzed by PTPs of both human and bacterial origin. The fluorogenic probe pCAP, was further used to synthesize positional-scanning synthetic combinatorial libraries (PS-SCL) of peptide substrates in order to determine the extended substrate specificities of various PTPs. Such a profile of substrate specificities readily shows both the similarities and differences between PTPs of the same family and those of different families. Furthermore, it was observed that replacing the fluorogenic probe in selective substrates with non hydrolyzable mimics of phosphotyrosine could result in potent, selective inhibitors. The substrate specificities determined from this study would be invaluable in the design of potent, selective PTP substrates and inhibitors for biochemical and therapeutic applications. Furthermore, these probes were used to design peptides for cellular imaging. The viability of the imaging principle using coumarin based probes was checked and various conditions for optimizing internalization of the peptides in cells were analyzed. The imaging technique would allow one to carry out high throughput screening for drugs in cells, and will have a wide impact on the fields of drug development and drug discovery.