Lowther, Jonathan and Robinson, Mark W. and Donnelly, Sheila M. and Xu, Weibo and Stack, Colin M. and Matthews, Jacqueline M. and Dalton, John P. (2009) The Importance of pH in Regulating the Function of the Fasciola hepatica Cathepsin L1 Cysteine Protease. PLoS Neglected Tropical Diseases, 3 (1). pp. 1-11. ISSN 1935-2727

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Abstract

The helminth parasite Fasciola hepatica secretes cathepsin L cysteine proteases to invade its host, migrate through tissues and digest haemoglobin, its main source of amino acids. Here we investigated the importance of pH in regulating the activity and functions of the major cathepsin L protease FheCL1. The slightly acidic pH of the parasite gut facilitates the auto-catalytic activation of FheCL1 from its inactive proFheCL1 zymogen; this process was ,40-fold faster at pH 4.5 than at pH 7.0. Active mature FheCL1 is very stable at acidic and neutral conditions (the enzyme retained ,45% activity when incubated at 37uC and pH 4.5 for 10 days) and displayed a broad pH range for activity peptide substrates and the protein ovalbumin, peaking between pH 5.5 and pH 7.0. This pH profile likely reflects the need for FheCL1 to function both in the parasite gut and in the host tissues. FheCL1, however, could not cleave its natural substrate Hb in the pH range pH 5.5 and pH 7.0; digestion occurred only at pH#4.5, which coincided with pH-induced dissociation of the Hb tetramer. Our studies indicate that the acidic pH of the parasite relaxes the Hb structure, making it susceptible to proteolysis by FheCL1. This process is enhanced by glutathione (GSH), the main reducing agent contained in red blood cells. Using mass spectrometry, we show that FheCL1 can degrade Hb to small peptides, predominantly of 4–14 residues, but cannot release free amino acids. Therefore, we suggest that Hb degradation is not completed in the gut lumen but that the resulting peptides are absorbed by the gut epithelial cells for further processing by intracellular di- and amino-peptidases to free amino acids that are distributed through the parasite tissue for protein anabolism.

Item Type:	Article
Keywords:	Importance of pH; Regulating Function; Fasciola hepatica; Cathepsin L1 Cysteine Protease;
Academic Unit:	Faculty of Science and Engineering > Biology
Item ID:	2179
Depositing User:	Colin Stack
Date Deposited:	13 Oct 2010 13:39
Journal or Publication Title:	PLoS Neglected Tropical Diseases
Publisher:	Public Library of Science
Refereed:	Yes
URI:	http://www.plosntds.org/home.action
Use Licence:	This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here

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