An evolutionary-based definition and classification of target evaluation units (EUs) is presented for the 14th round of the critical assessment of structure prediction (CASP14). CASP14 targets included 84 experimental models submitted by various structural groups (designated T1024–T1101). Targets were split into EUs based on the domain organization of available templates and performance of server groups. Several targets required splitting (19 out of 25 multidomain targets) due in part to observed conformation changes. All in all, 96 CASP14 EUs were defined and assigned to tertiary structure assessment categories (Topology-based FM or High Accuracy-based TBM-easy and TBM-hard) considering their evolutionary relationship to existing ECOD fold space: 24 family level, 50 distant homologs (H-group), 12 analogs (X-group), and 10 new folds. Principal component analysis and heatmap visualization of sequence and structure similarity to known templates as well as performance of servers highlighted trends in CASP14 target difficulty. The assigned evolutionary levels (i.e., H-groups) and assessment classes (i.e., FM) displayed overlapping clusters of EUs. Many viral targets diverged considerably from their template homologs and thus were more difficult for prediction than other homology-related targets. On the other hand, some targets did not have sequence-identifiable templates, but were predicted better than expected due to relatively simple arrangements of secondary structural elements. An apparent improvement in overall server performance in CASP14 further complicated traditional classification, which ultimately assigned EUs into high-accuracy modeling (27 TBM-easy and 31 TBM-hard), topology (23 FM), or both (15 FM/TBM).

中文翻译：

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第 14 轮蛋白质结构预测关键评估 (CASP14) 中的目标分类

为第 14 轮结构预测关键评估 (CASP14) 提出了基于进化的目标评估单元 (EU) 的定义和分类。CASP14 目标包括由各种结构组（指定为 T1024-T1101）提交的 84 个实验模型。根据可用模板的域组织和服务器组的性能，将目标拆分为 EU。部分由于观察到的构象变化，几个目标需要拆分（25 个多域目标中的 19 个）。总而言之，考虑到它们与现有 ECOD 折叠空间的进化关系，96 个 CASP14 EU 被定义并分配到三级结构评估类别（基于拓扑的 FM 或基于高精度的 TBM-easy 和 TBM-hard）：24 个家族级别，50 个远距离同系物（H 组）、12 个类似物（X 组）和 10 个新折叠。序列和结构与已知模板的相似性以及服务器性能的主成分分析和热图可视化突出显示了 CASP14 目标难度的趋势。指定的进化级别（即 H 组）和评估类别（即 FM）显示 EU 的重叠集群。许多病毒目标与其模板同系物有很大差异，因此比其他同源相关目标更难预测。另一方面，一些目标没有序列可识别的模板，但由于二级结构元素的排列相对简单，预测结果好于预期。CASP14 整体服务器性能的明显改善进一步复杂化了传统分类，最终将 EU 分配到高精度建模（27 个 TBM-easy 和 31 个 TBM-hard），