Editing Structural bioinformatics (section)

=== Structural alignment ===
[[Structural alignment]] is a method for comparison between 3D structures based on their shape and conformation.<ref>{{Cite web|url=https://www.sciencedaily.com/terms/structural_alignment.htm|title=Structural alignment (genomics)|website=ScienceDaily|language=en|access-date=2020-02-26}}</ref> It could be used to infer the evolutionary relationship among a set of proteins even with low sequence similarity. Structural alignment implies superimposing a 3D structure over a second one, rotating and translating atoms in corresponding positions (in general, using the ''C<sub>α</sub>'' atoms or even the backbone heavy atoms ''C'', ''N'', ''O'', and ''C<sub>α</sub>''). Usually, the alignment quality is evaluated based on the [[Root-mean-square deviation|root-mean-square deviation (RMSD)]] of atomic positions, ''i.e.'', the average distance between atoms after superimposition:

: <math>\mathrm{RMSD}=\sqrt{\frac{1}{N}\sum_{i=1}^N\delta_i^2}</math>

where ''δ<sub>i</sub>'' is the distance between atom ''i'' and either a reference atom corresponding in the other structure or the mean coordinate of the ''N'' equivalent atoms. In general, the RMSD outcome is measured in [[Ångström]] (Å) unit, which is equivalent to 10<sup>−10</sup> m. The nearer to zero the RMSD value, the more similar are the structures.