In bioinformatics, the template modeling score or TM-score is a measure of similarity between two protein structures with different tertiary structures. The TM-score is intended as a more accurate measure of the quality of full-length protein structures than the often used RMSD and GDT measures. The TM-score indicates the difference between two structures by a score between
(
0
,
1
]
, where 1 indicates a perfect match between two structures (thus the higher the better). Generally scores below 0.20 corresponds to randomly chosen unrelated proteins whereas structures with a score higher than 0.5 assume roughly the same fold. A quantitative study shows that proteins of TM-score = 0.5 have a posterior probability of 37% in the same CATH topology family and of 13% in the same SCOP fold family. The probabilities increase rapidly when TM-score > 0.5. The TM-score is designed to be independent of protein lengths.
TM-score
=
max
[
1
L
target
∑
i
L
aligned
1
1
+
(
d
i
d
0
(
L
target
)
)
2
]
where
L
target
and
L
aligned
are the lengths of the target protein and the aligned region respectively.
d
i
is the distance between the
i
th pair of residues and
d
0
(
L
target
)
=
1.24
L
target
−
15
3
−
1.8
is a distance scale that normalizes distances.
