Structural Difficulty (SD) Index
A Measure for Reliable Modelability of Protein Tertiary Structures

Where is the protein structure prediction field today or what is the success rate of best modeling softwares /servers for protein structure prediction ? Simple questions like these do not have simple and ready answers today. Conventional methods of explaining whether structure of a sequence is modelable in terms of homology based parameters do not reflect the current status of the field. There is more to structure prediction than mere homology. Similarity and identity based measures of modelability of a protein sequence may be misleading sometimes. “Structural Difficulty (SD)” index, which is derived from secondary structures, homology and physico-chemical features of protein sequences, reflects the capability of predicting good quality structures with some of the best methodologies available currently. The SD index also helps to assess the plausiblity for developing proteome level structural databases for various organisms.