Based on evolutionary phylogeny An up-to-date classification of protease evolutionary superfamilies is found in the MEROPS database. In this database, proteases are classified firstly by 'clan' (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 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 within the S1 family).
BasEd on eVoLutIonArY phyLogEny an uP-To-daTe clasSificAtion oF prOteASE eVolutiOnARY supeRfaMilies Is found In thE merOpS datAbase. in tHiS DatAbase, ProTeaseS aRE classifieD fiRstLy by 'Clan' (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 FAmIlies bASED on sequeNce sImilaritY (eG. 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 wIthIn thE s1 FamiLY).