Editing Structural bioinformatics (section)

=== Protein structure ===
{{main|Protein structure}}
The structure of a protein is directly related to its function. The presence of certain chemical groups in specific locations allows proteins to act as [[enzyme]]s, catalyzing several chemical reactions.<ref>{{Cite book|last1=Gu|first1=Jenny |last2=Bourne|first2=Philip E. | name-list-style = vanc |url=https://books.google.com/books?id=4H_ai7ivRIcC|title=Structural Bioinformatics|date=2009-03-16|publisher=John Wiley & Sons|isbn=978-0-470-18105-8|language=en}}</ref> In general, protein structures are classified into four levels: [[Protein primary structure|primary]] (sequences), [[Protein secondary structure|secondary]] (local conformation of the polypeptide chain), [[Protein tertiary structure|tertiary]]  (three-dimensional structure of the protein fold), and [[Protein quaternary structure|quaternary]] (association of multiple polypeptide structures). Structural bioinformatics mainly addresses interactions among structures taking into consideration their space coordinates. Thus, the primary structure is better analyzed in traditional branches of bioinformatics. However, the sequence implies restrictions that allow the formation of conserved local conformations of the polypeptide chain, such as [[alpha-helix]], [[Beta sheet|beta-sheets]], and loops (secondary structure<ref>{{cite journal | vauthors = Kocincová L, Jarešová M, Byška J, Parulek J, Hauser H, Kozlíková B | title = Comparative visualization of protein secondary structures | journal = BMC Bioinformatics | volume = 18 | issue = Suppl 2 | pages = 23 | date = February 2017 | pmid = 28251875 | pmc = 5333176 | doi = 10.1186/s12859-016-1449-z | doi-access = free }}</ref>). Also, weak interactions (such as [[hydrogen bond]]s) stabilize the protein fold. Interactions could be intrachain, i.e., when occurring between parts of the same protein monomer (tertiary structure), or interchain, i.e., when occurring between different structures (quaternary structure). Finally, the topological arrangement of interactions, whether strong or weak, and entanglements is being studied in the field of structural bioinformatics, utilizing frameworks such as [[circuit topology]].