TERMs (short for TERtiary Motifs) are compact modules that recur in protein structures and capture the effective degeneracy of secondary, tertiary, and quaternary structural environments in proteins. In Zheng et al.  we suggest that PDB-based TERM statistics represent fundamental relationships between sequence and structure. In Mackensie et al. , we show that the protein structural universe is highly degenerate ("quantized" so to speak) at the level of TERMs, and a surprisingly small number of such motifs describes the majority of known structure space.
 F. Zheng, J. Zhang, G. Grigoryan, "Tertiary Structural Propensities Reveal Fundamental Sequence/Structure Relationships", Structure, 23(5): 961-971, 2015.
 C. O. Mackenzie, J. Zhou, G. Grigoryan, "Tertiary Alphabet for the Observable Protein Structural Universe", Proceedings of the National Academy of Sciences, 113(47): E7438-E7447, 2016.
The following contains more information about specific TERM-related projects and results: