In vitro characterization of glutathione transferases from Sarcoptes scabiei

The mite Sarcoptes scabiei causes sarcoptic mange, or scabies, a disease that affects both animals and humans worldwide. The ectoparasite not only causes suffering in the host but also financial losses in e.g. pig herds. Infections can be cured with acaricides but treatment failures have been reported. Very little is known about drug detoxification in S. scabiei, and hence more information on underlying enzymatic mechanisms could prolong the lifespan of acaricides used in treatment of both animals and humans. The aim of this thesis was to characterize glutathione transferases (GSTs) from S. scabiei, investigate their possible involvement in resistance development and their potential as antigens in serology. GSTs are multifunctional enzymes with fundamental roles in the cellular detoxification, and these enzymes have been linked to drug resistance in various organisms. GSTs have also been suggested to confer acaricide resistance in S. scabiei. The first Delta GST occurring outside insects was identified, and phylogenetically classified. The crystal structure of this GST was also determined, which was the first Acari (mites and ticks) GST structure. The 3D-structures of two other Delta GSTs were predicted using homology modeling. Possible binding modes between the three Delta GSTs and various acaricides and the synergist diethyl maleate (DEM) were investigated using docking studies. Recombinant versions of the Delta GSTs and three Mu GSTs were biochemically characterized under steady-state conditions, and inhibition analyses with various acaricides and DEM were conducted. Additionally, the potential of the GSTs as antigens in serology was investigated. The results showed that all S. scabiei GSTs, except one, were catalytically active and significantly inhibited by various acaricides. However none of the GSTs were good antigens for serology. The docking studies showed that S. scabiei GSTs could metabolize or bind various acaricides, hence strengthening the suggestion that GSTs might confer resistance to acaricides in S. scabiei.