David Koes edited section_Query_Definition_As_a__.tex  about 8 years ago

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\subsection{Shape Queries}  Similarity of molecular shape is a common method of structure-based virtual screening \cite{Nicholls_2010}. Pharmit uses the Volumetric Aligned Molecular Shapes (VAMS) \cite{vams} method of shape search, which uses inclusive and exclusive shape constraints.  \cite{matchpack}\cite{vams}  Users have the option of using shape as an additional constraint on the similarity search. The ligand's surface or a set of user-defined spheres may be used as an inclusive constraint, the receptor's surface or a set of user-defined spheres may be used as an exclusive constraint, or both inclusive and exclusive shapes may be used. Multiple spheres may be defined for both inclusive and exclusive search by choosing the "Spheres" option in the dropdown menu and pressing "Add". This will display a menu allowing the user to set the position and size of the sphere. Pressing "Add" again will enable the user to continue adding spheres. The shape constraint is applied differently depending on whether it is used to search the database prior to pharmacophore filtering or to filter results returned by a pharmacophore search. In the former case, a shape search returns molecules in the search database that contain the entire included shape and do not overlap any part of the excluded shape. In the latter case, the results of the pharmacophore search are filtered by shape to ensure that at least one heavy atom falls within the inclusive shape and no heavy atom centers fall within any exclusive shape. In either case, the results of the initial search are aligned to that search for the secondary filtering - thus for a given molecule a pose may exist that allows it to meet the secondary filter, but it will not be returned if the aligned pose resulting from the initial search does not meet those constraints. Our recommendation is that users define both inclusive and exclusive shape constraints using the ligand and receptor surfaces and use them as secondary filtering on the results of a pharmacophore search. The order of application of pharmacophore and shape constraints can be swapped using the second button from the top of the left sidebar, which switches between "Pharmacophore Search → Shape Filter" and "Shape Search → Pharmacophore Filter".