1 | INTRODUCTION
CASP has been monitoring progress in the protein tertiary structure prediction for over 25 years1-4. Every other year since 1994, CASP organizers contact a wide network of structural biologists in quest of targets for the upcoming protein structure modeling experiment. The latest CASP15 call yielded 93 single-sequence entries representing monomeric proteins or subunits of protein multimeric complexes (https://predictioncenter.org/casp15/targetlist.cgi?view=regular). Eighty-one entries on this list were suggested for tertiary structure prediction, while the remaining twelve were auxiliary structures for other prediction categories (see Table 1). Four targets out of the 81 were canceled due to the lack of structure at the time of evaluation, leaving 77 for the assessment. Below we discuss procedures for splitting these targets into evaluation units (EUs) and assigning them to evolutionary-based prediction classes.
Defining and classifying evaluation units in CASP has been a very important and time-consuming task requiring multiple numerical tests and extensive human inspection. In five out of six recent CASPs these tasks were directed by Lisa Kinch, whose involvement with the structural classification ECOD database5 and extensive knowledge of protein structure was an invaluable asset6-10. In CASP15 we decided to develop a procedure that would mimic the procedure of previous CASPs while requiring only minimal human intervention.