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== Publication Abstract from PubMed ==

Oligopeptidases impose a size limitation on their substrates, the mechanism of which has long been in debate. Here we present the structure of a hexameric serine protease, an oligopeptidase from Pyrococcus horikoshii (PhAAP), revealing a complex, self-compartmentalized inner space, where substrates may access the monomer active sites passing through a double-gated "check-in" system: first passing through a pore on the hexamer surface, then turning to enter through an even smaller opening at the monomers' domain-interface. This substrate screening strategy is unique within the family. We found that among oligopeptidases a member of catalytic apparatus is positioned near an amylogenic beta-edge, which needs to be protected to prevent aggregation and found different strategies applied to such end. We propose that self-assembly within the family results in characteristically different substrate selection mechanisms coupled to different multimerization states.

A self-compartmentalizing hexamer serine protease from Pyrococcus horikoshii - substrate selection achieved through multimerization.,Menyhard DK, Kiss-Szeman A, Tichy-Racs E, Hornung B, Radi K, Szeltner Z, Domokos K, Szamosi I, Naray-Szabo G, Polgar L, Harmat V J Biol Chem. 2013 Apr 30. PMID:23632025<ref>PMID:23632025</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>

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== References ==

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