Editing Protease (section)

===Based on evolutionary phylogeny===
An up-to-date classification of protease evolutionary [[protein superfamily|superfamilies]] is found in the MEROPS database.<ref name="pmid19892822">{{cite journal | vauthors = Rawlings ND, Barrett AJ, Bateman A | title = MEROPS: the peptidase database | journal = Nucleic Acids Research | volume = 38 | issue = Database issue | pages = D227–D233 | date = January 2010 | pmid = 19892822 | pmc = 2808883 | doi = 10.1093/nar/gkp971 }}</ref> In this database, proteases are classified firstly by 'clan' ([[protein superfamily|superfamily]]) based on structure, mechanism and catalytic residue order (e.g. the [[PA clan]] where P indicates a mixture of nucleophile families). Within each 'clan', proteases are classified into [[protein family|families]] based on sequence similarity (e.g. the S1 and C3 families within the PA clan). Each family may contain many hundreds of related proteases (e.g. [[trypsin]], [[elastase]], [[thrombin]] and [[Streptogrisin A|streptogrisin]] within the S1 family).

Currently more than 50 clans are known, each indicating an independent evolutionary origin of proteolysis.<ref name="pmid19892822" />