page_title: PA clan of proteases
section_title: Structure
hierarchical_section_title: PA clan of proteases / Structure
caption_attribution_description: English: Structural homology in the PA superfamily (PA clan). The double beta-barrel that characterises the superfamily is highlighted in red. Shown are representative structures from several families within the PA superfamily. Note that some proteins show partially modified structural. Chymotrypsin (1gg6), thrombin (1mkx), tobacco etch virus protease (1lvm), calicivirin (1wqs), west nile virus protease (1fp7), exfoliatin toxin (1exf), HtrA protease (1l1j), snake venom plasminogen activator (1bqy), chloroplast protease (4fln) and equine arteritis virus protease (1mbm).
context_page_description: The PA clan is the largest group of proteases with common ancestry as identified by structural homology. Members have a chymotrypsin-like fold and similar proteolysis mechanisms but can have identity of <10%. The clan contains both cysteine and serine proteases. PA clan proteases can be found in plants, animals, fungi, eubacteria, archaea and viruses.
  The common use of the catalytic triad for hydrolysis by multiple clans of proteases, including the PA clan, represents an example of convergent evolution. The differences in the catalytic triad within the PA clan is also an example of divergent evolution of active sites in enzymes.
context_section_description: Despite retaining as little as 10% sequence identity, PA clan members isolated from viruses, prokaryotes and eukaryotes show structural homology and can be aligned by structural similarity (e.g. with DALI).
caption: Structural homology in the PA superfamily. The double beta-barrel that characterises the superfamily is highlighted in red. Shown are representative structures from several families within the PA superfamily. Note that some proteins show partially modified structural. Chymotrypsin (PDB: 1gg6​), thrombin (PDB: 1mkx​), tobacco etch virus protease (PDB: 1lvm​), calicivirin (PDB: 1wqs​), west nile virus protease (PDB: 1fp7​), exfoliatin toxin (PDB: 1exf​), HtrA protease (PDB: 1l1j​), snake venom plasminogen activator (PDB: 1bqy​), chloroplast protease (PDB: 4fln​) and equine arteritis virus protease (PDB: 1mbm​).
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