<a href="//commons.wikimedia.org/w/index.php?title=Structural_homology&amp;action=edit&amp;redlink=1" class="new" title="Structural homology (page does not exist)">Structural homology</a> in the <a href="//commons.wikimedia.org/w/index.php?title=PA_clan&amp;action=edit&amp;redlink=1" class="new" title="PA clan (page does not exist)">PA superfamily</a> (PA clan). The double beta-barrel that characterises the <a href="//commons.wikimedia.org/w/index.php?title=Superfamily&amp;action=edit&amp;redlink=1" class="new" title="Superfamily (page does not exist)">superfamily</a> is highlighted in red. Shown are representative structures from several families within the PA superfamily. Note that some proteins show partially modified structural. <a href="//commons.wikimedia.org/w/index.php?title=Chymotrypsin&amp;action=edit&amp;redlink=1" class="new" title="Chymotrypsin (page does not exist)">Chymotrypsin</a> (1gg6), <a href="//commons.wikimedia.org/w/index.php?title=Thrombin&amp;action=edit&amp;redlink=1" class="new" title="Thrombin (page does not exist)">thrombin</a> (1mkx), 
<a href="//commons.wikimedia.org/w/index.php?title=Tobacco_etch_virus_protease&amp;action=edit&amp;redlink=1" class="new" title="Tobacco etch virus protease (page does not exist)">tobacco etch virus protease</a> (1lvm), <a href="//commons.wikimedia.org/w/index.php?title=Calicivirin&amp;action=edit&amp;redlink=1" class="new" title="Calicivirin (page does not exist)">calicivirin</a> (1wqs), <a href="//commons.wikimedia.org/w/index.php?title=West_nile_virus&amp;action=edit&amp;redlink=1" class="new" title="West nile virus (page does not exist)">west nile virus</a> protease (1fp7), <a href="//commons.wikimedia.org/wiki/Staphylococcus_aureus#toxins" title="Staphylococcus aureus">exfoliatin toxin</a> (1exf), <a href="//commons.wikimedia.org/w/index.php?title=Peptidase_Do&amp;action=edit&amp;redlink=1" class="new" title="Peptidase Do (page does not exist)">HtrA protease</a> (1l1j), <a href="//commons.wikimedia.org/wiki/Trimeresurus_stejnegeri" title="Trimeresurus stejnegeri">snake venom plasminogen activator</a> (1bqy), <a href="//commons.wikimedia.org/wiki/Chloroplast" class="mw-redirect" title="Chloroplast">chloroplast</a> <a href="//commons.wikimedia.org/w/index.php?title=Peptidase_Do&amp;action=edit&amp;redlink=1" class="new" title="Peptidase Do (page does not exist)">protease</a> (4fln) and <a href="//commons.wikimedia.org/w/index.php?title=Equine_viral_arteritis&amp;action=edit&amp;redlink=1" class="new" title="Equine viral arteritis (page does not exist)">equine arteritis virus</a> protease (1mbm).
<a href="//commons.wikimedia.org/wiki/User:Evolution_and_evolvability" title="User:Evolution and evolvability">Thomas Shafee</a>
CC BY 4.0
<cite style="font-style:normal">Thomas, Shafee, (2014). "<a rel="nofollow" class="external text" href="https://www.repository.cam.ac.uk/handle/1810/245207">Evolvability of a viral protease: experimental evolution of catalysis, robustness and specificity</a>". <i>PhD Thesis</i>. University of Cambridge.</cite>