TM-score is an algorithm to calculate the similarity of topologies of two protein structures. It can be exploited to quantitatively access the quality of protein structure predictions relative to native. Because TM-score weights the close matches stronger than the distant matches, TM-score is more sensitive than root-mean-square deviation (RMSD) (An illustative example can be found from here). A single score between (0,1] is assigned to each comparison. Based on statistics, if a template/model has a TM-score around or below 0.17, it means the prediction is nothing more than a random selection from PDB library.

What is the difference between TM-score and TM-align? The TM-score program is to compare two models based on their given and known residue equivalency. It is usually NOT applied to compare two proteins of different sequences. The TM-align is a structural alignment program for comparing two proteins whose sequences can be different. The TM-align will first find the best equivalent residues of two proteins based on the structure similarity and then output a TM-score. The TM-score values in both programs have the same definition.

TM-score FAQ