2.1 | Defining evaluation units
Domains are basic folding units of proteins. They can be mobile, and their relative position can deviate depending on environmental conditions (e.g., the presence of a ligand), protein’s functional state (e.g., open or closed) or structure determination factors (e.g., crystal packing). Thus, evaluating models versus a specific domain conformation in a multi-domain structure can be too restrictive and penalizing. To address this issue, CASP adopted a domain-based approach to evaluating models, where multidomain targets are first split into smaller evaluation units. Even though the recent progress in modeling and the availability of non-rigid body structure comparison methods make splitting of targets into EUs less critical, we kept this practice to allow fair comparison of results across CASPs. A detailed procedure is described below.