2.1 | Scope of the experiment
In the Spring and Summer of 2022, CASP solicited 103 yet-to-be-published structures as potential modeling targets for the CASP15 experiment. The structures were provided by 48 structure determination groups from 14 countries all over the world. They include single-sequence protein molecules, protein-protein complexes, RNA molecules, RNA-protein complexes, and protein-ligand complexes. Ninety-eight proposed targets were deemed suitable for the CASP experiment and were gradually released for prediction over a period of three months (May 2 through July 29, 2022). Together with target sequences, predictors were provided the information on the oligomerization state of the targets and availability of bound organic ligands or ions (17). All in all, CASP15 offered 47 multimeric protein complexes for modeling in the Protein assembly category (40 assessed), 81 monomeric proteins or subunits of multimeric complexes in the Tertiary Structure category (77 assessed, divided into 112 Evaluation units (18)), 12 RNA structures in the RNA category, 23 protein-ligand complexes in the Ligand binding category, and two protein-RNA complexes. 89 research labs from 17 countries submitted models in one or more categories, with the USA (30 labs) and China (29 labs) most represented. Some labs created more than one participating group, so that 162 groups were assessed altogether. Of these, 56 are server groups, where target sequences are sent directly to a CASP-registered computer and a response is required within 72 hours. For non-server groups, usually there was a three-week window in which to submit models, allowing time for human intervention.