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A major cathepsin B protease from the liver fluke Fasciola hepatica has atypical active site features and a potential role in the digestive tract of newly excysted juvenile parasites

journal contribution
posted on 2024-11-01, 05:43 authored by Simone Beckham, David Piedrafita, Carolyn Phillips, Nirma Samarawickrema, Ruby H P Law, Peter SmookerPeter Smooker, Noelene Quinsey, James A Irving, Deanne Greenwood, S Verhelst, Matthew Bogyo, Boris Turk, Theresa Coetzer, L Wijeyewickrema, T W Spithill, Robert Pike
The newly excysted juvenile (NEJ) stage of the Fasciola hepatica lifecycle occurs just prior to invasion into the wall of the gut of the host, rendering it an important target for drug development. The cathepsin B enzymes from NEJ flukes have recently been demonstrated to be crucial to invasion and migration by the parasite. Here we characterize one of the cathepsin B enzymes (recombinant FhcatB1) from NEJ flukes. FhcatB1 has biochemical properties distinct from mammalian cathepsin B enzymes, with an atypical preference for Ile over Leu or Arg residues at the P2 substrate position and an inability to act as an exopeptidase. FhcatB1 was active across a broad pH range (optimal activity at pH 5.5-7.0) and resistant to inhibition by cystatin family inhibitors from sheep and humans, suggesting that this enzyme would be able to function in extracellular environments in its mammalian hosts. It appears, however, that the FhcatB1 protease functions largely as a digestive enzyme in the gut of the parasite, due to the localization of a specific, fluorescently labeled inhibitor with an Ile at the P2 position. Molecular modelling and dynamics were used to predict the basis for the unusual substrate specificity: a P2 Ile residue positions the substrate optimally for interaction with catalytic residues of the enzyme, and the enzyme lacks an occluding loop His residue crucial for exopeptidase activity. The unique features of the enzyme, particularly with regard to its specificity and likely importance to a vital stage of the parasite's life cycle, make it an excellent target for therapeutic inhibitors or vaccination.

History

Journal

International Journal of Biochemistry and Cell Biology

Volume

41

Issue

7

Start page

1601

End page

1612

Total pages

12

Publisher

Pergamon

Place published

United Kingdom

Language

English

Copyright

© 2009 Elsevier Ltd. All rights reserved.

Former Identifier

2006011892

Esploro creation date

2020-06-22

Fedora creation date

2010-11-19

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