The importance of pH in regulating the function of the Fasciola hepatica cathepsin L1 cysteine protease. Lowther, J., Robinson, M., Donnelly, S., Xu, W., Stack, C., Matthews, J., & Dalton, J. PLoS Neglected Tropical Diseases, 2009. cited By 65
The importance of pH in regulating the function of the Fasciola hepatica cathepsin L1 cysteine protease [link]Paper  doi  abstract   bibtex   
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 37°C 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. © 2009 Lowther et al.
@ARTICLE{Lowther2009,
author={Lowther, J. and Robinson, M.W. and Donnelly, S.M. and Xu, W. and Stack, C.M. and Matthews, J.M. and Dalton, J.P.},
title={The importance of pH in regulating the function of the Fasciola hepatica cathepsin L1 cysteine protease},
journal={PLoS Neglected Tropical Diseases},
year={2009},
volume={3},
number={1},
doi={10.1371/journal.pntd.0000369},
art_number={e369},
note={cited By 65},
url={https://www.scopus.com/inward/record.uri?eid=2-s2.0-65549085704&doi=10.1371%2fjournal.pntd.0000369&partnerID=40&md5=11a33428cfc92f3715c9984b899f6e38},
affiliation={Institute for the Biotechnology of Infectious Diseases (IBID), University of Technology Sydney (UTS), Sydney, NSW, Australia; School of Molecular and Microbial Biosciences, University of Sydney, Sydney, NSW, Australia; Department of Medical Microbiology, University of Western Sydney (UWS), Narellan Road, Campbelltown, NSW, Australia},
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 37°C 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. © 2009 Lowther et al.},
keywords={amino acid;  aminopeptidase;  cathepsin L;  cysteine proteinase;  dipeptidase;  enzyme precursor;  glutathione;  hemoglobin;  ovalbumin;  tetramer;  cathepsin;  cathepsin L1, Fasciola hepatica;  hemoglobin, animal cell;  animal tissue;  article;  controlled study;  dissociation;  enzyme activation;  enzyme activity;  enzyme degradation;  enzyme substrate;  erythrocyte;  Fasciola hepatica;  incubation time;  intestine absorption;  intestine epithelium cell;  mass spectrometry;  nonhuman;  pH;  protein degradation;  protein secretion;  protein synthesis;  regulatory mechanism;  animal;  enzymology;  Fasciola hepatica;  metabolism, Animals;  Cathepsins;  Fasciola hepatica;  Hemoglobins;  Hydrogen-Ion Concentration},
correspondence_address1={Lowther, J.; Institute for the Biotechnology of Infectious Diseases (IBID), , Sydney, NSW, Australia},
pubmed_id={19172172},
language={English},
abbrev_source_title={PLoS. Negl. Trop. Dis.},
document_type={Article},
source={Scopus},
}

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