Inactivation of Tritrichomonas Foetus and Schistosoma Mansoni Purine Phosphoribosyltransferases by Arginine‐Specific Reagents

Abstract

The arginine-specific reagents phenylglyoxal and butane-2,3-dione irreversibly inactivate the Tritrichomonas foetus hypoxanthine-guanine-xanthine phosphoribosyltransferase (HGXPRT) and Schistosoma mansoni hypoxanthine-guanine phosphoribosyltransferase (HGPRT). The inactivation of the tritrichomonal enzyme by phenylglyoxal follows time-dependent and concentration-dependent pseudo-firstorder kinetics. Complete protection against inactivation is afforded by the addition of 25 pM GMP, whereas 5-phosphoribosyl-1-diphosphate (PRibPP) at 50-250 pM can only slow down the inactivation, without being protective. Digestion of [7-'4C]phenylglyoxal-modified enzyme with trypsin and separation of the peptides by reverse-phase HPLC shows that only one radioactive peak is greatly diminished by incubation with 25 pM GMP or 1 mM PRibPP. Mass-spectral analysis identifies Arg155 as the target site of two molecules of phenylglyoxal that is protected by the substrates. This amino acid residue is positioned next to Tyr156, which is a highly conserved aromatic residue among all the purine phosphoribosyltransferases (PRT) and is always found stacked on top of the purine substrate. This may explain why phenylglyoxal labeling of Arg155 inactivates the enzyme and why GMP can protect Arg155 more effectively than PRibPP. Among the purine PRT in our possession, only schistosomal HGPRT, the only other enzyme that contains an arginine residue at the corresponding location (Arg187), was susceptible to phenylglyoxal and butane-2,3-dione. The presence of Lys185-Phe186 and Ser179-Trp180 at the corresponding locations in human HGPRT and Giardia lamblia GPRT, respectively, may explain their resistance to phenylglyoxal. Thus, Arg155 in 7: foetus HGXPRT and Arg187 in S. mansoni HGPRT will be attractive targets for future studies.

Bioinformatic Analysis of Helicobacter pylori XGPRTase: A Potential Therapeutic Target

“…The 6‐oxopurine PRTase of a number of organisms have been studied in depth, and in some parasites they have been identified as potential therapeutic targets owing to the absence in these organisms of a de novo purine synthesis pathway, which makes salvage pathways essential for survival. Parasites whose phosphoribosyltransferases have been investigated include Tritrichomonas foetus [11,12] , Giardia lamblia [13,14] , Plasmodium falciparum [15] , Toxoplasma gondii [16] , Schistosoma mansoni [17], and Trypanosoma cruzi [18,19] . The crystal structures of many members of the PRTase family have been resolved in both the absence and the presence of substrates, products, and transition‐state inhibitors.…”

Comparative study of excretory–secretory proteins released by Schistosoma mansoni-resistant, susceptible and naïve Biomphalaria glabrata

“…The potential immunosuppressive properties of this protein have not been studied yet. Phosphoribosyltransferase has been identified as essential to nucleotide metabolism, though nicotinate phosphoribosyltransferase has yet to be subject to much analysis [84, 85]. The specific role of proline-serine-threonine phosphatase interacting protein in S. mansoni is still unknown.…”

Pyrimidine metabolism in schistosomes: A comparison with other parasites and the search for potential chemotherapeutic targets

“…Studies on the biological, chemical and pharmacological aspects of pyrimidine metabolism in various organisms, from prokaryotes to mammalian systems, are numerous and have been discussed in several reviews by O’Donovan and Neuhard (1970), Henderson and Paterson (1973), Levine et al (1974), Jaffe (1975), Hurst (1980), Jones (1980), Kensler and Cooney (1981), Munch-Peterson (1983), Hammond and Gutteriddge (1984), Hassan and Coombs (1988), Evans and Guy (2004), Hyde (2007), Garavito et al (2015), and Krungkrai and Krungkrai (2016). However, in contrast to the relatively extensive work on purine metabolism in schistosomes (Senft et al, 1972, 1973a and 1973b; Stegman et al, 1973; Crabtree and Senft, 1974; Miech et al, 1975; Levy and Read, 1975a and 1975b; Senft and Crabtree, 1983; el Kouni et al, 1983a, 1985, 1987 and 1989; Dovey, et al, 1984 and 1985; el Kouni and Cha, 1987; Baer et al, 1988; el Kouni, 1991; Craig III et al, 1991; Yuan et al, 1993; Kanaaneh et al, 1994: Kanaani et al, 1995 and 1997; Foulk et al, 2002; Pereira et al, 2003, 2005, 2010a and 2010b; da Silveira et al, 2004; Yang et al, 2007; Castilho et al, 2010; D’Muniz-Pereira et al, 2011; Postigo et al, 2010; Marques-Ide et al, 2012; de Moraes et al, 2013; Romanello et al, 2013 and 2017; Saverese and el Kouni, 2014; Torini et al, 2016; Zeraik et al, 2017), little information is available on pyrimidine metabolism in this parasite.…”