Molecular Cloning, Biochemical Characterization, and Partial Protective Immunity of the Heme-Binding Glutathione S -Transferases from the Human Hookworm Necator americanus

Abstract

ABSTRACT Hookworm glutathione S -transferases (GSTs) are critical for parasite blood feeding and survival and represent potential targets for vaccination. Three cDNAs, each encoding a full-length GST protein from the human hookworm Necator americanus (and designated Na -GST-1, Na -GST-2, and Na -GST-3, respectively) were isolated from cDNA based on their sequence similarity to Ac -GST-1, a GST from the dog hookworm Ancylostoma caninum . The open reading frames of the three N. americanus GSTs each contain 206 amino acids with 51% to 69% sequence identity between each other and Ac -GST-1. Sequence alignment with GSTs from other organisms shows that the three Na -GSTs belong to a nematode-specific nu-class GST family. All three Na -GSTs, when expressed in Pi chia pastoris , exhibited low lipid peroxidase and glutathione-conjugating enzymatic activities but high heme-binding capacities, and they may be involved in the detoxification and/or transport of heme. In two separate vaccine trials, recombinant Na -GST-1 formulated with Alhydrogel elicited 32 and 39% reductions in adult hookworm burdens ( P < 0.05) following N. americanus larval challenge relative to the results for a group immunized with Alhydrogel alone. In contrast, no protection was observed in vaccine trials with Na -GST-2 or Na -GST-3. On the basis of these and other preclinical data, Na -GST-1 is under possible consideration for further vaccine development.