Characterization of the peptide substrate specificity of glutathionylspermidine synthetase from Crithidia fasciculata.
Trypanothione, a metabolite specific to trypanosomatid parasites, is enzymatically synthesized from spermidine and glutathione by the consecutive action of the ATP-dependent carbon-nitrogen ligases, glutathionylspermidine synthetase and trypanothione synthetase. As part of our programme aimed at developing inhibitors of these enzymes, we have synthesized a series of analogues of glutathione (gamma-L-Glu-L-Cys-Gly) and tested them as substrates or inhibitors of glutathionylspermidine synthetase. Recognition at the gamma-glutamyl moiety appears to be essential, as any modification of this part of glutathione results in a total loss of activity as a substrate. Alkylation of the thiol side chain of cysteine with methyl, ethyl or propyl groups yields analogues with catalytic efficiencies (kcat/Km) as substrates equivalent to or better than glutathione. In contrast, the bulkier S-butyl analogue was a much poorer substrate. Substitution of L-Cys by amino acids with an alkyl side-chain is also well tolerated giving relative catalytic efficiencies of 1.1 and 1.5 for peptide analogues containing L-Val and L-Ile respectively. Other analogues, where the bulk of the alkyl chain is increased further (as in L-Leu or L-Phe) or where the glycine moiety is replaced with L-Ala, are inhibitors rather than substrates.
De Craecker
S
S
Department of Pharmaceutical Chemistry, University of Antwerp (UIA), Belgium.
Verbruggen
C
C
Rajan
P K
PK
Smith
K
K
Haemers
A
A
Fairlamb
A H
AH
D019732:Amide Synthases; D000818:Animals; D016831:Crithidia fasciculata / Q000201:enzymology*; D005978:Glutathione / Q000031:analogs & derivatives* / Q000096:biosynthesis; D008025:Ligases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015800:Protozoan Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013095:Spermidine / Q000031:analogs & derivatives* / Q000096:biosynthesis; D013379:Substrate Specificity
D015800:Protozoan Proteins; C044809:trypanothione; D008025:Ligases; D019732:Amide Synthases; C081536:glutathionylspermidine synthetase; D005978:Glutathione; D013095:Spermidine