title: USRCAT: real-time ultrafast shape recognition with pharmacophoric constraints.
abstract: BACKGROUND
  Ligand-based virtual screening using molecular shape is an important tool for researchers who wish to find novel chemical scaffolds in compound libraries. The Ultrafast Shape Recognition (USR) algorithm is capable of screening millions of compounds and is therefore suitable for usage in a web service. The algorithm however is agnostic of atom types and cannot discriminate compounds with similar shape but distinct pharmacophoric features. To solve this problem, an extension of USR called USRCAT, has been developed that includes pharmacophoric information whilst retaining the performance benefits of the original method.
  
  
  RESULTS
  The USRCAT extension is shown to outperform the traditional USR method in a retrospective virtual screening benchmark. Also, a relational database implementation is described that is capable of screening a million conformers in milliseconds and allows the inclusion of complex query parameters.
  
  
  CONCLUSIONS
  USRCAT provides a solution to the lack of atom type information in the USR algorithm. Researchers, particularly those with only limited resources, who wish to use ligand-based virtual screening in order to discover new hits, will benefit the most. Online chemical databases that offer a shape-based similarity method might also find advantage in using USRCAT due to its accuracy and performance. The source code is freely available and can easily be modified to fit specific needs.
authors.affiliation: Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, CB2 1GA, Cambridge, United Kingdom. ams214@cam.ac.uk.
authors.forename: Adrian M
authors.initials: AM
authors.lastname: Schreyer
authors.forename: Tom
authors.initials: T
authors.lastname: Blundell