title: Use of activity-based probes to develop high throughput screening assays that can be performed in complex cell extracts.
abstract: BACKGROUND
  High throughput screening (HTS) is one of the primary tools used to identify novel enzyme inhibitors. However, its applicability is generally restricted to targets that can either be expressed recombinantly or purified in large quantities.
  
  
  RESULTS
  Here, we described a method to use activity-based probes (ABPs) to identify substrates that are sufficiently selective to allow HTS in complex biological samples. Because ABPs label their target enzymes through the formation of a permanent covalent bond, we can correlate labeling of target enzymes in a complex mixture with inhibition of turnover of a substrate in that same mixture. Thus, substrate specificity can be determined and substrates with sufficiently high selectivity for HTS can be identified. In this study, we demonstrate this method by using an ABP for dipeptidyl aminopeptidases to identify (Pro-Arg)2-Rhodamine as a specific substrate for DPAP1 in Plasmodium falciparum lysates and Cathepsin C in rat liver extracts. We then used this substrate to develop highly sensitive HTS assays (Z'>0.8) that are suitable for use in screening large collections of small molecules (i.e >300,000) for inhibitors of these proteases. Finally, we demonstrate that it is possible to use broad-spectrum ABPs to identify target-specific substrates.
  
  
  CONCLUSIONS
  We believe that this approach will have value for many enzymatic systems where access to large amounts of active enzyme is problematic.
authors.affiliation: Department of Pathology, Stanford School of Medicine, Stanford, California, United States of America.
authors.forename: Edgar
authors.initials: E
authors.lastname: Deu
authors.forename: Zhimou
authors.initials: Z
authors.lastname: Yang
authors.forename: Flora
authors.initials: F
authors.lastname: Wang
authors.forename: Michael
authors.initials: M
authors.lastname: Klemba
authors.forename: Matthew
authors.initials: M
authors.lastname: Bogyo
mesh_terms: D000818:Animals; D020789:Cathepsin C / Q000037:antagonists & inhibitors / Q000378:metabolism; D002457:Cell Extracts; D004353:Drug Evaluation, Preclinical / Q000379:methods*; D057166:High-Throughput Screening Assays / Q000379:methods*; D006801:Humans; D008099:Liver / Q000166:cytology; D015335:Molecular Probes / Q000378:metabolism*; D010963:Plasmodium falciparum / Q000166:cytology; D011480:Protease Inhibitors / Q000494:pharmacology; D051381:Rats; D054852:Small Molecule Libraries / Q000494:pharmacology; D013379:Substrate Specificity
chemical_list: D002457:Cell Extracts; D015335:Molecular Probes; D011480:Protease Inhibitors; D054852:Small Molecule Libraries; D020789:Cathepsin C