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The hemoglobins of the trematodes Fasciola hepatica and Paramphistomum epiclitum: A molecular biological, physico-chemical, kinetic, and vaccination study

¹ Department of Biomedical Science, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium
² Department of Physics, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium
³ Institut National de la Santé et de la Recherché Médicale (INSERM), Unité U779, 94276 Le Krêmlin-Bicêtre, France
⁴ Department of Virology, Parasitology, and Immunology, Faculty of Veterinary Medicine, Ghent University, 9820 Merelbeke, Belgium
⁵ Department of Physics, CNISM and Centre of Excellence for Biomedical Research, University of Genova, 16136 Genova, Italy
⁶ Department of Biomolecular Sciences and Biotechnology, CIMAINA and CNR-INFM, University of Milano, 20133 Milano, Italy

(RECEIVED May 20, 2008; FINAL REVISION June 19, 2008; ACCEPTED June 20, 2008)

The trematode Fasciola hepatica (Fa.he.) is a common parasite of human and livestock. The hemoglobin (Hb) of Fa.he., a potential immunogen, was chosen for characterization in the search for an effective vaccine. Characterization of trematode Hbs show that they are intracellular single-domain globins with the following remarkable features: (1) Fa.he. expresses two Hb isoforms that differ at two amino acid sites (F1: 119Y/123Q; F2: 119F/123L). Both isoforms are monoacetylated at their N-termini; (2) the genes coding for Fa.he. and Paramphistomum epiclitum (Pa.ep.) Hbs are interrupted by two introns at the conserved positions B12.2 and G7.0.; (3) UV/VIS and resonance Raman spectroscopy identify the recombinant Fa.he. HbF2 as a pentacoordinated high-spin ferrous Hb; (4) electron paramagnetic resonance spectroscopy of cyano-met Fa.he. HbF2 proves that the endogenously bound imidazole has no imidazolate character; (5) the major structural determinants of the globin fold are present, they contain a TyrB10/TyrE7 residue pair on the distal side. Although such distal-site pair is a signature for high oxygen affinity, as shown for Pa.ep. Hb, the oxygen-binding rate parameters for Fa.he. Hb are intermediate between those of myoglobin and those of other trematode Hbs; (6) the three-dimensional structure of recombinant Fa.he. HbF2 from this study closely resembles the three-dimensional structure of Pa.ep. determined earlier. The set of distal-site polar interactions observed in Pa.ep. Hb is matched with small but significant structural adjustments; (7) despite the potential immunogenic character of the fluke Hb, vaccination of calves with recombinant Fa.he. HbF2 failed to promote protection against parasitic infection.

Keywords: hemoglobins; fluke; ligand binding; 3D structure; spectroscopy; vaccination

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